Derby City Council v UYR [2025] EWCA Civ 1648:
No “Strong Prima Facie Case” Threshold for Interim Relief in Age Assessment Judicial Review, and the Effect of Existing Section 20 Accommodation

1. Introduction

The Court of Appeal’s decision in Derby City Council v UYR [2025] EWCA Civ 1648 is an important authority in two closely related areas of public law and children’s law:

the correct test for granting interim relief in judicial review challenges to age assessments; and
how the balance of convenience should be approached where a claimant is already being accommodated as a child by one local authority (B), but seeks interim relief against another local authority (A) which conducted an earlier age assessment.

The judgment clarifies that, in age assessment judicial review proceedings:

there is no gateway requirement that the claimant show a “strong prima facie case” before obtaining interim relief. The familiar American Cyanamid test applies: it is enough that there is a serious issue to be tried;
where the claimant is already being accommodated as a child by a different local authority under section 20 Children Act 1989, and there is no real risk that this accommodation will cease, the balance of convenience will generally not justify mandatory interim relief against the original assessing authority; and
while concurrent section 20 duties may arise, the question who pays is not normally part of the court’s balancing exercise when deciding interim relief as between the claimant and one particular local authority.

This decision therefore both:

settles an area of doctrinal uncertainty about the merits threshold in age assessment interim relief; and
gives practical guidance on disputes between local authorities over interim responsibility for unaccompanied putative children.

2. Factual and Procedural Background

2.1 The claimant’s journey and initial treatment as an adult

The claimant, UYR, is an Ethiopian national who arrived in the UK on 17 March 2025. He claimed to be born on 6 October 2009, making him 15 at the time of arrival. His account included the murder of his father in Ethiopia, subsequent imprisonment with his brother, a period in detention, an escape via Libya and Italy, and eventual arrival in the UK hidden in a lorry.

On arrival, he told police he was 15. The following sequence occurred:

He was taken to Yarl’s Wood immigration removal centre.
On 18 March 2025, social workers from Bedford Borough Council carried out a brief age assessment and concluded he was “clearly an adult”, so no full “Merton-compliant” assessment was undertaken.
He was dispersed to adult asylum accommodation and moved to Derby four days later.
Approaching Derby City Council (Derby CC) and again asserting he was a child, he triggered another brief age assessment by Derby CC on 28 March 2025. Derby CC reached the same conclusion as Bedford: he was clearly an adult and should be supported by the Home Office as such.
On 23 April 2025, the Home Office moved him to adult accommodation in the Manchester area.

2.2 Intervention by Manchester City Council

On or about 6 May 2025, UYR collapsed and was admitted to A&E at a hospital in Manchester. A staff nurse considered he looked “very young” and made a safeguarding referral to Manchester City Council (Manchester CC). He was admitted to a children’s ward.

Emergency duty social workers from Manchester CC decided to accommodate him as a child under section 20 Children Act 1989, apparently without knowledge of the earlier age assessments and without conducting their own assessment. Since then, he has been in foster care arranged by Manchester CC, save for a further hospital admission for tuberculosis.

2.3 Judicial review and interim relief before the deputy judge

On 2 May 2025, before the Manchester hospital episode, UYR had already issued a claim for judicial review of Derby CC’s age assessment decision, together with an application for interim relief seeking to be treated and accommodated as a child by Derby.

By the time of the interim relief hearing on 14 May 2025:

Manchester CC was already accommodating him in foster care as a child;
Manchester CC had by then discovered Derby’s earlier age assessment and the fact it was being challenged; and
Manchester CC indicated (in an email to the court) that:
- they were currently accommodating the claimant, but
- in light of the ADCS Joint Working Guidance and ADCS Age Assessment Guidance, the claimant should be referred back to the local authority that conducted the previous age assessment (here, Derby), and that no agreement had yet been reached between authorities.

The deputy High Court judge (Karen Ridge, sitting as a deputy judge of the High Court) applied the three-limb test from American Cyanamid v Ethicon [1975] AC 396 and ordered interim relief requiring Derby CC to:

“treat the Claimant as a putative child aged 15 … and … secure that the Claimant is provided with accommodation, care and support pursuant to section 20 of the Children Act 1989” within 14 days.

She reasoned that:

There was a serious issue to be tried as to age, in light of Manchester CC’s and hospital professionals’ views treating him as a child.
Damages would be inadequate for either party.
The balance of convenience favoured treating him as a child, particularly given his deteriorating mental health, medical evidence and the fact that the status quo was that he was being accommodated as a child.
It was not sufficient to decline relief simply because Manchester CC was already accommodating him: there was “no guarantee” they would continue to do so, and Derby CC would be the proper authority with section 20 responsibility if their age assessment proved to be wrong (drawing on HA v Hillingdon [2012] EWHC 291 (Admin)).

She nevertheless stayed the order until September 2025 given the claimant’s existing foster placement with Manchester CC.

3. The Appeal and Issues Before the Court of Appeal

3.1 Grounds of appeal

Derby CC appealed on two grounds:

Ground 1: The deputy judge erred in principle by granting interim relief without finding that the claimant had a “strong prima facie case” on the merits, which Derby argued was a threshold (gateway) requirement for interim mandatory relief in public law cases.
Ground 2: The judge erred in her assessment of the balance of convenience by ordering Derby CC to provide section 20 accommodation when:
- (a) the claimant was already being accommodated as a child by Manchester CC and this was not properly weighed in considering prejudice;
- (b) the judge held that Manchester CC could rely on the Joint Working Guidance in looking to Derby;
- (c) Manchester CC had already accepted and treated the claimant as a child before knowing that Derby’s assessment was being challenged; and
- (d) R (HA) v Hillingdon LBC did not, Derby said, deal with a situation where a second authority has independently accepted a person as a child.

The deputy judge granted permission to appeal on ground 2 only, but Phillips LJ subsequently granted permission on ground 1 as well and extended the stay, on condition that Manchester CC continued to accommodate the claimant in Manchester as a child.

3.2 Respondent’s notice and Manchester CC’s position

By a respondent’s notice, the claimant argued that the deputy judge’s decision should be upheld on these additional bases:

There is no threshold requirement of a “strong prima facie case” in age assessment interim relief claims;
If such a test existed, the deputy judge had in fact found it met on the facts; and
In any event, a strong prima facie case was established on the evidence.

Manchester CC, though only an interested party below, actively supported the continuation of interim relief, but primarily on the basis that:

Derby CC, having conducted the age assessment, retained responsibility for the claimant should he prove to be a child; and
Any interim order should fall on Derby, even if in practical terms Manchester continued to host the foster placement, funded by Derby CC.

4. Summary of the Judgment

The Court of Appeal (Zacaroli LJ giving the lead judgment, with Yip LJ and Moylan LJ agreeing) held as follows:

Ground 1 (Merits threshold): dismissed.
In age assessment judicial review claims, there is no gateway requirement for the claimant to establish a “strong prima facie case” as a condition of obtaining interim relief. The correct merits test is the American Cyanamid standard of a serious issue to be tried, or “real prospect of success”. The strength of the case remains a factor in the overall balance, but there is no separate elevated threshold in age assessment cases.
Ground 2 (Balance of convenience): allowed.
The deputy judge had correctly concluded that, absent Manchester’s involvement, the claimant should be treated and accommodated as a child pending the age determination. However, she had proceeded on a mistaken premise that Manchester CC’s ongoing provision of section 20 accommodation was precarious and could cease at any moment. On the proper analysis:
- Manchester CC had accepted a section 20 duty and could not lightly abandon it without undertaking its own age assessment; and
- there was no real risk that the claimant would cease to be accommodated as a child pending the outcome of the judicial review.
Accordingly, there was no need for interim relief against Derby CC. The correct outcome at the interim stage was that the claimant remain in his existing foster placement through Manchester CC, without imposing additional mandatory obligations on Derby CC.

The Court stressed that:

Questions of who ultimately bears the financial burden between local authorities are not part of the balancing exercise between the claimant and Derby CC on an application for interim relief; and
the case is concerned solely with interim relief, not with the ultimate question of who will be found to owe the substantive section 20 duty once the claimant’s age is finally determined.

5. Legislative and Policy Framework

5.1 Children Act 1989 duties

The Court rehearsed the relevant statutory provisions:

Section 17(1)(a): general duty on every local authority to safeguard and promote the welfare of children in need in their area.
“Child” is defined in s.105(1) as a person under 18.
Section 17(10): defines when a child is “in need”, including where, without the provision of services, their health or development would be at risk or impaired.
Section 20(1): imposes a duty to provide accommodation for any child in need within the local authority’s area who appears to require accommodation because:
- no one has parental responsibility;
- they are lost or abandoned; or
- their carer cannot provide suitable accommodation or care.
Section 27: creates a mechanism for inter-authority co-operation, allowing one authority to request help from another where that would assist in fulfilling its Part III functions, with a corresponding duty to comply if compatible with the assisting authority’s own obligations.

There was no dispute that if UYR is under 18, then as an unaccompanied migrant he is a child in need attracting section 20 duties.

5.2 Joint Working Guidance on Age Assessment

The Court considered the Age Assessment Joint Working Guidance (2023), issued by the Home Office and the Association of Directors of Children’s Services (ADCS). Key points:

Local authorities must work together and prioritise safeguarding, consistently with the Children Act 1989 and Children Act 2004.
Where conflicting age assessments arise between authorities, the Home Office should notify the authorities so they can agree which authority should take responsibility.
Where new relevant information arises after an age assessment by Authority A and the individual has moved to Authority B, the guidance suggests that the matter should be referred back to Authority A and an agreement reached about which authority will reassess the age.
The guidance recognises that age assessment decisions may be challenged by judicial review and the court may make a declaration in rem (binding on all agencies) as to age: see R (S) v Croydon LBC [2011] EWHC 2091 (Admin).

The Court accepted this guidance as part of the factual context, but made clear that it does not determine the allocation of legal responsibility for interim relief by itself.

6. Precedents Cited and Their Influence on the Decision

6.1 The American Cyanamid framework in public law

The starting point was American Cyanamid Co v Ethicon Ltd [1975] AC 396, which established the now-classic test for interim injunctions:

Is there a serious issue to be tried? (i.e. the claim is not frivolous or vexatious and has a real prospect of success);
Would damages be an adequate remedy for either party if the injunction were wrongly granted or refused?
Where does the balance of convenience lie?

In R (Medical Justice) v Secretary of State for the Home Department [2010] EWHC 1425 (Admin), Cranston J held that these principles apply in judicial review, adapted to the public law context. He noted that “serious issue to be tried” is equivalent to having a real prospect of success, and adopted the reasoning of Smith v ILEA [1978] 1 All ER 411, which equated the two formulations.

Zacaroli LJ adopted this Medical Justice framework for judicial review generally and applied it to age assessment cases, save for recognising specific features of age assessment which influence the merits threshold and the balance of convenience.

6.2 De Falco and Francis: the “strong prima facie case” line

Derby CC relied heavily on a line of authority beginning with De Falco v Crawley BC [1980] QB 460 and followed in Francis v Kensington and Chelsea RLBC [2003] 1 WLR 2248.

De Falco: claimants, found intentionally homeless, sought an interim injunction compelling the council to accommodate them pending judicial review. Lord Denning MR and Bridge LJ held that American Cyanamid did not assist and that the court should not grant a mandatory injunction unless the claimants made out a “strong prima facie case” that the decision was invalid. Bridge LJ tied this higher requirement to:
- the impossibility of recovering accommodation costs from the applicants;
- the risk of disrupting the authority’s housing allocation priorities; and
- the potentially serious impact on others on the housing list.
Francis: applied De Falco in the context of interim appeals under s.204A Housing Act 1996, again requiring a strong prima facie case for mandatory relief against a housing authority. The Court of Appeal linked this to the traditional view that mandatory injunctions require a higher standard than prohibitory ones.

Derby CC argued that this line, recently endorsed in RRR (see below), applied equally to mandatory interim relief in age assessment cases.

6.3 National Commercial Bank v Olint and the “barren” mandatory/prohibitory distinction

In National Commercial Bank Jamaica Ltd v Olint Corp Ltd [2009] UKPC 16; [2009] 1 WLR 1405, Lord Hoffmann explained that:

The core principle for interim injunctions, whether mandatory or prohibitory, is to choose the course likely to cause the least irremediable prejudice to either party.
The classification of an injunction as “mandatory” or “prohibitory” is often barren in practical terms; what matters is the concrete prejudice likely to arise.
However, in cases where an injunction would cause significant prejudice to the defendant, the court may require a “high degree of assurance” (Megarry J’s phrase in Shepherd Homes Ltd v Sandham [1971] Ch 340) that it will prove to have been rightly granted at trial.

Zacaroli LJ used this to undermine any rigid rule that all interim mandatory relief requires a strong prima facie case, emphasising that a higher assessment of the merits is context- and consequence-dependent, not a formal gateway.

6.4 British Standards Institution v RRR Manufacturing (2024) and De Falco’s continuing status

The Court engaged with the recent decision of the Court of Appeal in British Standards Institution v R (RRR Manufacturing Pty Ltd) [2024] EWCA Civ 530. In RRR:

The appellant argued, relying on De Falco, that a strong prima facie case was a threshold condition for mandatory interim relief in public law.
Elisabeth Laing LJ held that:
- the court’s interim relief jurisdiction in judicial review stems from s.31 Senior Courts Act 1981 and its historical prerogative jurisdiction;
- the court applies, by analogy, American Cyanamid (rather than some wholly distinct regime);
- De Falco has not been overruled, and in general, the “strong prima facie case” approach still stands in its own context; but
- she expressly noted that age assessment disputes form a “rare example” where the court itself determines the facts on judicial review, and that they are treated differently (para 87).
Nugee LJ agreed that De Falco still requires a strong prima facie case for certain mandatory relief against public authorities and that this can operate as a threshold requirement.

Zacaroli LJ placed particular weight on Laing LJ’s express carving out of age assessment cases from the reach of De Falco, using this as a platform to hold that, even if De Falco remains good law in its own sphere, it does not apply to age assessment interim relief.

6.5 Factortame, Ofsted, and reluctance to rigid “strong case” rules

The Court also drew on:

R v Secretary of State for Transport, ex p Factortame Ltd (No 2) [1991] 1 AC 603, in which Lord Goff doubted any absolute rule that a claimant must always show a strong prima facie case to obtain interim relief against the enforcement of a statute. He emphasised:
- the need for a flexible discretion having regard to all circumstances; and
- the possibility that severe and irreparable harm might justify interim relief even where the claimant’s prospects are not very strong.
R (X) v Ofsted [2020] EWCA Civ 594, where Lindblom LJ accepted that, in public law, courts are often reluctant to grant interim relief without a strong prima facie case, but stopped short of endorsing any fixed threshold test. He treated the strength of the merits as a factor in the balance, not as a gateway.

These authorities supported the Court’s rejection of a rigid “strong prima facie” threshold, particularly in the specialised context of age assessment.

6.6 Age assessment case law: fact-finding and section 20 allocation

(a) Objective fact-finding role of the court

In R (A) v Croydon LBC [2009] UKSC 8; [2009] 1 WLR 2557, the Supreme Court held that:

a person’s age is an objective fact which the court can and must determine; and
in age assessment challenges, the court is not merely reviewing the rationality or legality of the local authority’s decision, but is itself the primary decision-maker on the fact of age.

This is crucial. Most judicial reviews involve deferential review of a public authority’s discretionary judgment, but age assessment claims are a fact-finding jurisdiction in which the weight accorded to the local authority’s view is much reduced. This significantly undermines the policy arguments that normally justify a high merits threshold for mandatory interim relief.

(b) Allocation of section 20 duties between local authorities

The Court considered two key authorities in disputes about which authority owes section 20 responsibilities for an unaccompanied child:

Liverpool CC v Hillingdon LBC [2009] EWCA Civ 43; [2009] PTSR 1067
K, a Pakistani national, claimed to be 15, was initially assessed by Liverpool as 18, and later found by an immigration judge (based on medical evidence) to be a child. He ended up physically in Hillingdon, which accommodated him but then, at his request, returned him to Liverpool without conducting its own age assessment.
- The Court of Appeal held that Hillingdon owed a section 20 duty once K was in its area and could not discharge that duty simply by shipping him back to Liverpool without proper assessment.
- Importantly, the court recognised the possibility of concurrent section 20 duties (Rix LJ at [44]).
- Zacaroli LJ noted that the mandatory order there was directed at Hillingdon, which had accepted and then abdicated responsibility without a lawful basis.
R (HA) v Hillingdon LBC [2012] EWHC 291 (Admin)
HA, an Afghan asylum seeker claiming to be 14, was treated by Hillingdon as a child initially, then later assessed as an adult and moved to Birmingham by UKBA. HA challenged the age assessment. Hillingdon argued that any duty now lay with Birmingham, where HA resided.
- Bean J rejected the notion of a purely geographical test for section 20 duties, emphasising Parliament cannot have intended children to be “passed from pillar to post” while authorities argued about responsibility.
- He held that, pending determination of the age assessment’s lawfulness, interim relief should be ordered against the original assessing authority (Hillingdon).

Bean J’s approach was influenced by R (G) v Southwark LBC [2009] 1 WLR 1299, where Lady Hale stressed that:

local authorities must look after children in their area irrespective of habitual residence;
they may later recoup costs from another authority; but
there should be no more passing children from pillar to post while authorities dispute who is responsible.

In Derby CC v UYR, these cases underpin:

the recognition that Derby CC may well be found to owe a section 20 duty retrospectively from the date of its age assessment if that assessment is overturned; and
the acceptance that concurrent section 20 duties (Derby and Manchester) may arise, at least on an interim basis.

(c) Age assessment interim relief at first instance

A further cluster of first-instance age assessment cases—BG v Oxfordshire CC [2014] EWHC 3187 (Admin), AS v Liverpool CC [2021] EWHC 3531 (Admin), and KKA v Cheshire East Council [2024] EWHC 575 (Admin)—had moved away from De Falco in the age assessment context.

Most notably, in AS v Liverpool, Nicol J held:

“There is no hard and fast rule that a claimant like AS must show a strong prima facie case, even though the relief sought might be characterised as a mandatory injunction … that characterisation is one factor which can properly be taken into account in assessing the balance of convenience. The strength of the claimant's claim … is also a factor to be taken into account in the balance of convenience.”

Fordham J in KKA synthesised this line, concluding that there is no higher threshold of a strong prima facie case for interim relief in age assessment matters, and that the court’s provisional view of the merits is a factor for the balance of justice, not a Gateway test.

Zacaroli LJ endorsed this first-instance trend and elevated it to binding Court of Appeal authority, expressly distinguishing age assessment from the De Falco/Francis/RRR line.

7. The Court’s Legal Reasoning

7.1 Ground 1: No “strong prima facie case” threshold in age assessment interim relief

(a) Context: age assessment as fact-finding, not deferential review

The Court’s key analytical move is to recognise the uniquely factual nature of age assessment judicial review, per R (A) v Croydon. Unlike most judicial reviews:

the court does not defer to the local authority’s assessment of age;
it will ultimately decide the claimant’s age as an objective fact at trial; and
the usual reasons for demanding a high merits threshold — such as respect for public authority decision-making or concern about intruding on resource-allocation judgments — are less compelling.

(b) Why De Falco and Francis do not dictate a threshold in age assessment cases

Zacaroli LJ accepts that:

De Falco and Francis remain good law in their own sphere, and
RRR confirms that, in some public law cases, a strong prima facie case may indeed be required for mandatory relief.

However, he identifies several reasons why the “strong prima facie” gateway is out of place in age assessment interim relief:

Objective fact, not discretionary judgment.
In ordinary judicial review, the court’s intervention is constrained by deference to the primary decision-maker. Requiring a strong case to justify interim interference can be rationalised by that deference. In age assessment, however, the court is itself the fact-finder on age and not simply reviewing for irrationality or legal error. There is no equivalent justification for a higher merits threshold.
Limited relevance of damages.
One justification advanced in De Falco was that damages are not an adequate remedy in judicial review cases. But this is symmetrical—it applies to both sides and does not, in itself, mandate a higher threshold. It is better understood as part of the broader balance of convenience analysis.
Distinction between housing allocation and children’s services.
In De Falco, a key concern was that ordering accommodation for a particular adult applicant could unfairly distort a finite housing allocation system, disadvantaging others awaiting allocation. By contrast, section 20 Children Act duties towards children in need are not capped in this way: the authority is obliged to accommodate every qualifying child, irrespective of how many others there are. While there is a financial burden, there is no direct trade-off with another child’s entitlement.
Explicit exclusion in RRR.
Elisabeth Laing LJ in RRR expressly noted that age assessment cases are a “rare example” in which the test for permission and interim relief is different because the court determines facts itself. This is strong support for placing age assessments outside the De Falco regime.

(c) Result: American Cyanamid test applies without a heightened gateway

The Court concludes at [59]:

“I reject the submission that there is a threshold requirement, upon an application for interim relief in a claim for judicial review of an age assessment, that there must be a strong prima facie claim. The threshold question is that derived from the first stage of the American Cyanamid test: is there a serious issue to be tried?”

The strength of the claim may still feature as part of the balancing exercise, especially where interim relief risks serious prejudice to the authority, but it is not elevated into a stand-alone gateway.

Zacaroli LJ also notes that, had it been necessary, the facts here—medical professionals and Manchester CC social workers accepting the claimant as a child without formal age assessment—would in any event justify describing the case as “strong prima facie” ([61]).

7.2 Ground 2: Balance of convenience where another authority is already accommodating the claimant

(a) Derby’s acceptance of general principles, but dispute on their application

Derby CC did not challenge the general proposition that, if the claimant were not already being accommodated, the balance of convenience in an age assessment case would usually favour treating him as a child pending trial. They accepted that:

a wrongly-treated child as an adult can suffer significant, potentially irreparable harm; and
damages are an inadequate remedy for such harm.

Their case on appeal was narrow but important:

Given that Manchester CC was already accommodating the claimant as a child, under section 20, and there was no real risk of that ceasing, there was no practical need for an order against Derby CC.
The deputy judge erred by treating Manchester CC’s provision as precarious and by relying on the ADCS Joint Working Guidance and the absence of a “guarantee” Manchester would continue accommodation.

(b) Manchester CC’s stance and concurrent duties

Manchester CC accepted in the Court of Appeal that:

It was currently subject to a section 20 duty in respect of the claimant;
It could not lawfully simply “walk away” from that duty; at minimum, it would need to conduct its own age assessment before altering his status; and
It would be “invidious” to remove a young person settled in foster care from that placement, especially during pending judicial review proceedings.

Zacaroli LJ accepted that:

Derby CC may also owe a concurrent section 20 duty, if its age assessment is ultimately found to be wrong, and
there is no conceptual reason why two local authorities could not owe concurrent duties (consistent with Rix LJ’s indication in Liverpool v Hillingdon and the Joint Working Guidance).

But the existence of concurrent duties is analytically separate from the question:

“Is it necessary or appropriate to impose a mandatory interim order on Derby CC, given that the claimant’s immediate welfare needs are already being met by Manchester CC?”

(c) The deputy judge’s error: mischaracterising Manchester’s position as precarious

Zacaroli LJ identifies two reasons why the deputy judge’s premise of precariousness was mistaken:

The contemporaneous email from Manchester CC.
Manchester’s email to the court recorded that emergency duty social workers had “decided to accommodate the Claimant after he was discharged from hospital”. This was an unconditional assumption of responsibility; it was only later that Manchester became aware of the earlier age assessments and sought to reach agreement with Derby CC. There was no suggestion that initial accommodation was “without prejudice” or merely stop-gap.
Legal inability to unilaterally cease section 20 accommodation.
Once Manchester had accepted the claimant as a child and begun accommodating him under section 20, it could not lawfully terminate that accommodation without:
- undertaking an age assessment; and
- potentially exposing itself to judicial review of any decision adverse to the claimant.
Given this, the prospect that Manchester would stop accommodating the claimant while the age issue was actively before the court was “remote”.

Furthermore, Manchester’s own submissions in the Court of Appeal—emphasising it would be invidious to move the claimant and seeking an order requiring Derby to fund existing foster care—reinforced the assessment that Manchester had no real intention to withdraw accommodation.

(d) Lady Hale’s “pillar to post” warning and its application here

The Court invoked Lady Hale’s warning in G v Southwark against passing children “from pillar to post” while authorities argue about responsibility. Here, that principle supports:

leaving the claimant in his existing foster placement with Manchester CC at the interim stage; and
rejecting solutions which would have the effect of disrupting that stability in pursuit of an abstract allocation of legal responsibility.

However, the Court also drew a line:

Lady Hale’s comments do not justify compelling an additional authority (here, Derby) to assume section 20 responsibility at the interim stage where the child’s needs are already met and where there is no risk of the child being moved.

(e) Financial disputes are not part of the claimant–Derby balance

A central point in the reasoning is that, when applying American Cyanamid between the claimant and Derby CC, the court is balancing:

the risk of harm to the claimant if relief is refused; and
the prejudice to Derby CC if relief is granted.

Since the claimant’s welfare needs (accommodation, care and support) were:

already being fully met by Manchester CC under section 20; and
unlikely to cease in the interim,

the claimant faced no practical harm from refusing relief against Derby CC.

By contrast, ordering Derby CC to provide or fund accommodation:

would potentially impose duplicative obligations, and
would embroil the court in resolving an inter-authority funding dispute which neither authority had formally put in issue before the court in these proceedings.

The Court makes clear that:

“It is no part of the balancing exercise between the claimant and Derby CC to consider who – as between Derby CC and Manchester CC – should be liable for the cost of the claimant’s interim accommodation.” ([93])

Therefore, while Derby and Manchester may well have competing arguments about which of them should bear cost and responsibility in the longer term, that is a separate matter, not to be determined via the claimant’s interim relief application.

8. Clarifying Complex Legal Concepts

8.1 “Serious issue to be tried” vs “strong prima facie case”

Serious issue to be tried (American Cyanamid):
- a relatively low threshold;
- the claim is not frivolous or vexatious and has a real (not fanciful) prospect of success.
Strong prima facie case:
- a significantly higher standard;
- the claimant’s case appears, on the interim material, clearly and strongly likely to succeed at trial.

In Derby CC v UYR, the Court rejects the idea that age assessment interim relief requires the higher standard as a gateway. It reinstates the ordinary serious issue test, while allowing the underlying strength of the case to influence the third limb of the test (balance of convenience).

8.2 Interim mandatory relief

An injunction is often called “mandatory” when it requires the defendant to take positive action (here, to provide accommodation and support), as opposed to “prohibitory” injunctions which simply prevent a party from acting in a certain way.

Historically, courts have often required a higher merits standard for mandatory injunctions, but Olint and Factortame caution against making this an inflexible rule. Instead, courts assess the real-world consequences of granting or withholding relief.

In this case, the Court accepts that the relief against Derby was “mandatory” in form but refuses to attach a rigid, elevated merits test to that classification in the age assessment context.

8.3 “Balance of convenience” in public law

The balance of convenience is the stage at which the court compares:

the harm or prejudice if relief is wrongly refused; and
the harm or prejudice if relief is wrongly granted.

In public law, this includes:

the impact on safety, welfare and rights of individuals;
the impact on the authority’s ability to perform its statutory functions; and
the public interest in lawful and orderly discharge of statutory duties.

In age assessment:

harm to a child wrongly treated as an adult is usually substantial and irremediable (e.g., exposure to adult asylum accommodation, loss of support, safeguarding risks);
harm to a local authority wrongly required to treat someone as a child is typically financial and administrative (though not trivial).

Where a child is already being safely accommodated under section 20 by one authority (Manchester), and the court is asked to impose duties on another (Derby), the balance of convenience must focus on:

whether granting relief adds anything in terms of protection to the claimant (here it did not); and
whether it would inappropriately force the court into a resource-allocation or funding dispute between authorities (which it should generally avoid at interim stage).

8.4 Section 20 Children Act 1989 and “putative” children

Section 20 requires local authorities to accommodate children in need who lack parental care or suitable accommodation. In practice, its application to age-disputed individuals generates the concept of a “putative child”: someone who claims to be under 18, whose age has not yet been definitively determined.

Prior case law (e.g. R (S) v Croydon [2017] EWHC 2656 (Admin), per Lavender J) and statutory guidance have suggested that, absent cogent reasons to the contrary, a putative child should be treated as a child pending proper assessment. The Court in Derby CC v UYR acknowledges these principles but treats them as relevant to the balance of convenience (limb three) rather than the merits threshold (limb one).

8.5 “Declaration in rem” in age assessment cases

A “declaration in rem” is a declaration of a legal or factual status that is binding not just between the immediate parties to the proceedings but against the world (all persons and agencies).

In age assessment cases, a High Court or Upper Tribunal declaration that a claimant was, on a given date, aged X is typically treated as a declaration in rem, binding:

all local authorities;
the Home Office; and
other public agencies.

The Joint Working Guidance explicitly refers to this, ensuring consistent treatment of the young person once a court has finally decided their age.

9. Impact and Significance of the Judgment

9.1 Clarifying the law on interim relief in age assessment judicial review

The most immediate impact is doctrinal clarity: age assessment judicial review claims are now expressly exempt from the De Falco-inspired requirement for a “strong prima facie case” as a gateway to interim mandatory relief.

For practitioners:

Applicants for interim relief in age assessment cases need only show a serious issue to be tried on age.
Authorities cannot resist interim relief solely on the basis that the claimant’s case is not “strong” in the De Falco sense.
The strength of the claimant’s case remains relevant at the balance of convenience stage, but not as an absolute precondition.

This should reduce unproductive arguments about whether a “strong prima facie” threshold applies in age assessment cases, and allow courts to focus on substantive factors: the claimant’s vulnerability, the nature of current accommodation, safeguarding issues, and practical risks.

9.2 Guidance where multiple local authorities are involved

The judgment also offers practical guidance on how courts should proceed where:

one authority (A) has carried out an age assessment and concluded the claimant is an adult; and
another authority (B), independently, has accepted the claimant as a child and is already providing section 20 accommodation.

Key implications:

If Authority B is already accommodating the claimant as a child, and there is no real risk that B will cease to do so before the age dispute is resolved, there will usually be no justification for imposing interim mandatory relief on Authority A.
The claimant cannot generally insist on relief specifically against Authority A merely to:
- shift the financial burden from B to A; or
- secure a preferred authority, where core welfare needs are already being met.
Courts will be reluctant to use interim relief applications as a vehicle to resolve funding or allocation disputes between local authorities, especially where those disputes have not been formally pleaded or joined.
At the same time, authorities must avoid “dumping” children or manipulating geography to evade duties: the Liverpool v Hillingdon, HA v Hillingdon and G v Southwark principles still apply.

This should encourage local authorities to follow the Joint Working Guidance in good faith—resolving which authority will assess and support the young person—without expecting the court to reallocate costs at the interim stage simply because one authority wishes another to step in.

9.3 Safeguarding and the “pillar to post” concern

The judgment reinforces the strong judicial aversion to moving vulnerable young people between placements during ongoing legal disputes:

Children should not be passed “from pillar to post” merely because authorities are arguing about who is responsible or who pays.
Where a claimant is already settled in foster care and is being treated as a child, the interim solution will almost always be to maintain that status quo, unless there is some clear safeguarding reason to do otherwise.

This has a stabilising effect on practice: it disincentivises “gaming” by either authorities or claimants through moving locations to achieve a more favourable assessment or to shift costs.

9.4 Relationship with UNCRC and domestic guidance

Although Article 3 of the UN Convention on the Rights of the Child (best interests as a primary consideration) and domestic statutory guidance on treating putative children as children are noted, the Court is careful not to:

transform those principles into a merits threshold; or
use them to justify imposing duties on multiple authorities where the child’s practical needs are already satisfied.

Instead, those instruments are seen as informing the balance of convenience analysis:

They help explain why, absent existing safe accommodation, interim relief will usually favour treating the claimant as a child.
But once a suitable placement as a child exists, the best interests of the child may point to remaining in that placement, not necessarily to shifting responsibility to another authority.

9.5 Litigation strategy for future age assessment cases

Practically, the decision affects both sides’ strategies:

For claimants:
- Interim relief should be sought primarily where there is no existing section 20 accommodation or where that accommodation is genuinely at risk.
- Where already accommodated as a child by one authority, claimants may find it difficult to obtain interim relief against another authority solely to secure a change in provider or to anticipate a future finding of retrospective responsibility.
For local authorities:
- An authority which has already accepted a child under section 20 is in a weak position to argue it can simply cease support without a proper age assessment.
- Authorities should expect courts to regard existing placements as stable unless clear evidence suggests otherwise.
- Age assessments and inter-authority negotiations should be conducted with the expectation that, at least until final determination, courts will concentrate on protecting the child’s welfare, not apportioning blame or cost.

10. Conclusion

Derby City Council v UYR is a significant decision for public law and children’s practitioners dealing with age-disputed unaccompanied migrants.

Its central contributions are:

Clarification of the merits test for interim relief in age assessment cases.
The Court of Appeal confirms that:
- There is no threshold requirement for a “strong prima facie case” in such cases.
- The correct approach is the American Cyanamid test, adapted to public law:
  1. Is there a serious issue to be tried on age?
  2. Are damages inadequate?
  3. Where does the balance of convenience lie?
- The strength of the merits may influence the balance of convenience but is not a gateway.
Guidance on the balance of convenience where another authority is already accommodating the claimant.
Where a claimant is already:
- accommodated as a child by another local authority under section 20, and
- there is no real risk that such accommodation will cease,
the court will ordinarily decline to impose mandatory interim relief on the original assessing authority. The inter-authority funding or responsibility dispute is not usually part of the court’s balancing exercise in the claimant’s application.
Reaffirmation of safeguarding and anti–“pillar to post” principles.
The judgment reinforces that:
- the primary concern is the child’s stability and welfare;
- children should not be shuffled between authorities and placements due to disputes over responsibility; and
- once an authority has accepted a section 20 duty, it cannot easily cast it aside without proper process.

Taken together, these principles provide a coherent framework for courts and practitioners addressing interim relief in age assessment disputes. The decision preserves flexibility and child-centred decision-making, while reducing unnecessary satellite litigation over thresholds and inter-authority cost-shifting at the interim stage.

Derby City Council v UYR [2025] EWCA Civ 1648: No “Strong Prima Facie Case” Threshold for Interim Relief in Age Assessment Judicial Review, and the Effect of Existing Section 20 Accommodation