Mathurin: Clarification vs Cross-Examination—When Judicial Interventions Render a Conviction Unsafe Despite a Strong Prosecution Case

Introduction

In Mathurin, R. v [2025] EWCA Crim 1254, the Court of Appeal (Criminal Division), per the Vice-President, quashed a conviction for supplying a Class A drug and ordered a retrial. The appeal succeeded on a single ground: the trial judge’s interventions during the defendant’s cross-examination crossed the line from permissible clarification into impermissible “testing” of the defence case, conveying judicial scepticism to the jury and thereby undermining the fairness of the trial.

The judgment revisits and firmly applies the principles in R v Inns [2018] EWCA Crim 1081; (2019) 1 Cr App R 5 concerning the role of a judge in an adversarial criminal trial. It clarifies that:

Even where the prosecution evidence is strong,
Even where the defence case is implausible and the defendant failed to mention it under caution,
Even where the judge’s summing-up is legally impeccable and expressly reminds the jury that the judge is not a “13th juror”,

a conviction may nonetheless be unsafe if judicial interventions during cross-examination have the effect of entering the arena and appearing to take sides on a central credibility issue.

Background and Key Facts

The appellant was convicted on 11 July 2024 of supplying a Class A drug. The factual matrix, largely agreed, was as follows:

Police prepared to execute a warrant at a flat occupied by Banda and Stubbs.
The appellant arrived in a van and interacted briefly with Banda (who cycled to the van); the appellant then entered the flat carrying a Footasylum drawstring bag and exited minutes later without it.
An hour later, police found just under 1kg of heroin inside a plastic bag placed within a blue shopping bag, itself inside a black Footasylum bag. The appellant’s fingerprints were found on the outside Footasylum bag but not on the interior bags containing the drugs.
More than an hour after leaving, the appellant returned to the flat; upon encountering a plain-clothed officer at the door, he ran but was detained.
Propensity evidence: the prosecution adduced a previous drugs conviction against the appellant.
Banda pleaded guilty to supplying a Class A drug; no evidence was offered against Stubbs; the appellant was tried alone.

The defence case: the appellant said he visited for legitimate reasons—to return an electric scooter charger Banda wished to borrow and to drop off Banda’s tools stored in the van. He said he placed the charger in the Footasylum bag, left it in the hallway on the first visit, forgot to give the tools, and returned later to seek Banda’s help with the heavy tool bag. When the door was answered by an unknown man (in fact a police officer), he panicked and ran. He had not mentioned this account when interviewed under caution.

Summary of the Judgment

The Court of Appeal allowed the appeal, quashed the conviction, and ordered a retrial. It held that the trial judge’s repeated interventions during cross-examination went beyond clarification and amounted to testing the appellant’s account in a way that highlighted weaknesses and conveyed scepticism to the jury. This constituted an impermissible “entry into the arena” that undermined the fairness of the trial.

Although the trial judge’s summing-up was fair and contained model directions (including the admonition that the judge is “not a 13th juror”), and although the prosecution case was strong, the conviction was nonetheless unsafe because the central issue for the jury was the credibility of the appellant’s explanation. The judge’s interventions significantly weakened the defence on that central issue.

Consequential orders:

Conviction quashed; retrial ordered on count 1 (supplying a Class A drug).
Direction to serve a fresh indictment in accordance with CrimPR r 10.82 within 28 days.
Appellant to be rearraigned within 2 months.
Retrial to take place at Snaresbrook Crown Court before a different judge (the original judge no longer sitting there).
No reporting restrictions deemed necessary; bail application to be considered promptly at a Crown Court mention hearing.

Analysis

Precedents Cited and Their Influence

The Court expressly relied on and endorsed the six “fundamentals” articulated by Singh LJ in R v Inns [2018] EWCA Crim 1081; (2019) 1 Cr App R 5, a case raising similar concerns about judicial interventions that were said to be tantamount to entering the arena. The six fundamentals, as summarised in Inns and quoted in Mathurin, are:

The jury, and only the jury, is the tribunal of fact in the Crown Court.
Our system is adversarial, not inquisitorial; the judge must act as a neutral umpire and must not appear to take sides.
Judges may ask questions to assist the jury, typically to clarify points, preferably at the end of a witness’s evidence where possible.
In an adversarial system, it is for the prosecution to prove its case and to cross-examine a defendant who elects to give evidence; it is not the judge’s role to cross-examine the defendant.
Defendants are entitled to present their account through their own advocate without constant interruption; excessive judicial interventions risk distorting the defence case.
Even if a defence seems implausible, it is for the prosecution to expose its weaknesses in cross-examination; unwarranted judicial interventions may be counterproductive.

In Mathurin, the Court did more than recite Inns; it applied those fundamentals to the trial transcript. The critical move was to differentiate between permissible “clarification” and impermissible “testing” that takes on the character of advocacy against the defendant. The Court concluded that several of the judge’s questions did not clarify prior evidence but instead introduced new lines of challenge, pointing out alternative courses of action and implicitly questioning the plausibility of the appellant’s account.

Legal Reasoning

The essence of the Court’s legal reasoning is threefold:

The line between clarification and cross-examination: While limited judicial questions may be put to clarify points for the jury, questions that posit alternative scenarios, highlight inconsistencies, or invite evaluative judgments on plausibility move from neutral clarification into adversarial testing. In Mathurin, examples included:
- “Did he not have [a charger] himself?”
- “Any particular reason to put it in a bag? Why not just hand it over as you took it?”
- “You did not say to him, ‘It’s in the back of the van, just grab it and then shut the door’?”
- “At that point, did he say, ‘What about the tools, mate?’”
- “Would it not be quicker to take them with you then rather than go in, get him, and come back again?”
- “Presumably not all builders go around in twos carrying tools.”
The Court characterised these as testing the account and pointing out weaknesses, rather than elucidating prior testimony.
Appearance matters: Whether or not the judge subjectively intended only to clarify, the effect on a reasonable jury is pivotal. The Court found the interventions would have left the jury with the impression that the judge was sceptical of the defence—“an impermissible entry into the arena” suggestive of taking sides. The Court emphasised that it is “nothing to the point” that counsel might have asked similar questions; the vice lies in the judge, not a party advocate, asking them.
Safety of the conviction despite strong evidence and a fair summing-up: The Court acknowledged:
- The prosecution case was strong (movement of the bag, fingerprints, return and flight, context of a 1kg heroin seizure, and propensity evidence).
- The appellant’s explanation was “already implausible” and was further weakened by his failure to advance it when questioned under caution.
- The appellant gave his evidence-in-chief without undue interruption, and the summing-up was fair and orthodox (including the direction that the judge is not a “13th juror”).
Nevertheless, the decisive consideration was issue-centrality: the jury could only convict if sure the appellant’s account was untrue. The defendant’s credibility on that critical issue was central, and the judge’s interventions “significantly weakened” that credibility before the jury. The appellate court “was not able to say that the conviction remains safe.”

The Court also dealt, with sensitivity, with trial dynamics. It recognised the practical difficulty for defence advocates deciding when to object to a judge’s interventions. When defence counsel sought to raise a matter in the absence of the jury, the judge continued with the evidence, saying “We are just dealing with evidence now.” This did not become a determinative ground in its own right, but it contextualised the cumulative effect of the interventions and the defence position.

Impact and Prospective Significance

Mathurin does not invent new doctrine; it forcefully applies Inns in a concrete, common scenario—judicial questions during a defendant’s cross-examination. The case will resonate in future appeals and trial practice for several reasons:

Clarification redefined with sharper boundaries: The decision underscores that “clarification” is narrowly confined to elucidating prior evidence for the jury. Questions framed as “why didn’t you do X?” or which posit reasonableness alternatives will usually be testing, not clarifying.
Strength of the prosecution case is not a fail-safe: Even strong evidence and a fair summing-up will not immunise a conviction if judicial interventions unfairly skew the jury’s assessment of a central credibility issue.
Perception of neutrality is substantive: The mere appearance of partiality or scepticism can vitiate the safety of the verdict where credibility is central. Judicial tone and sequencing—especially during the defendant’s cross-examination—carry outsized trial effects.
Short, defendant-centric trials carry heightened risk: Where few live witnesses appear and the defendant’s account is the fulcrum, intrusive judicial questions can disproportionately influence outcomes.
Practical litigation consequences: Defence counsel should consider timely applications to address judicial interventions in the jury’s absence and, if necessary, seek a specific direction reminding the jury that any judicial questions are solely for clarification and should not be taken as indicating any view on credibility. Judges should consider deferring questions until the end of a witness’s testimony and keeping interventions sparse, neutral, and truly clarificatory.

Complex Concepts Simplified

Unsafe conviction: On appeal, the court must quash a conviction if it considers it unsafe. “Unsafe” does not require proof of bias or a specific legal error; it is a broad fairness-based test. If judicial conduct may have materially undermined the fairness of the trial or the reliability of the verdict, the conviction can be unsafe.
Adversarial vs inquisitorial: In England and Wales, the prosecution and defence present their cases; the judge ensures fairness and legality but does not investigate or build the case. Judges should refrain from assuming the role of an advocate.
Judicial “entry into the arena”: A metaphor for when judges move beyond neutral case management and adopt an adversarial posture—e.g., cross-examining a defendant, suggesting answers, or projecting scepticism—creating a real risk of influencing the jury.
Summing-up and the “13th juror”: A trial judge summarizes the evidence and directs the law for the jury. A standard caution is that the judge’s views on the facts do not matter—the jury alone are arbiters of fact. However, a correct summing-up does not cure prejudicial interventions earlier in the trial if their effect on the jury’s view of credibility is significant.
Propensity evidence: Prior convictions can be admitted to show a relevant propensity (e.g., involvement in drug supply). Propensity evidence can strengthen a prosecution case but does not justify judicial cross-examination from the bench.
Failure to mention under caution: When a suspect omits an account during police interview and later advances it at trial, the jury may, in appropriate circumstances, be invited to draw an adverse inference about credibility. In Mathurin, this factor weakened the defence, but it did not salvage the conviction in the face of improper judicial interventions.
Retrial orders and CrimPR: When a conviction is quashed, the Court of Appeal may order a retrial. In Mathurin, the Court directed service of a fresh indictment within 28 days in accordance with CrimPR r 10.82 and re-arraignment within two months. It also indicated venue (Snaresbrook Crown Court) and addressed bail and reporting restrictions.

Key Passages and Their Significance

Several passages from the transcript crystallised the Court’s concerns. The judge’s questions:

Suggested alternative reasonable behaviour (“Why not just hand it over?”; “Would it not be quicker to take them with you?”), which are classic prosecutorial challenges, not neutral clarifications.
Raised scenarios not previously the subject of the witness’s answer (“Did he not have one himself?”; “Presumably not all builders go around in twos carrying tools”), intimating disbelief.
Invited the prosecutor to pick up the same line of challenge, giving an appearance—however unintentional—of judge and prosecutor operating in tandem.

The Court accepted that some interventions were clarifying and that the judge did not intend to overstep. Nevertheless, the cumulative effect on the jury’s view of the defendant’s credibility on the central issue was decisive.

Practice Guidance Drawn from Mathurin

For Trial Judges

Intervene sparingly, and preferably at the end of a witness’s evidence, unless immediate clarification is truly necessary for comprehension.
Confine questions to clarifying what has already been said; avoid hypotheticals, “why didn’t you…?” challenges, and statements suggesting reasonableness standards or alternative behaviour.
Be especially cautious during a defendant’s cross-examination, where the prosecution has the structured opportunity to challenge credibility.
Remain alert to the optics: tone, repetition, and alignment with a party’s case may be perceived as partiality.

For Advocates

Object promptly and respectfully to judicial questions that cross into testing; request to address the court in the absence of the jury if necessary.
Seek corrective directions making clear that judicial questions are for clarification only and do not indicate any view of the facts or credibility.
Record and preserve the pattern of interventions for appeal; cumulative effect often matters more than any single question.
Where interventions continue, invite the judge to defer further questions until the end of a witness’s testimony to avoid interrupting the defence narrative.

Conclusion

Mathurin is a careful but firm reaffirmation of the Inns fundamentals governing judicial interventions in criminal trials. Its primary contribution is to show that the fairness of the trial—and thus the safety of the conviction—can be compromised by judicial questioning that crosses from clarification into adversarial testing, even where:

The prosecution evidence is strong,
The defence is implausible and was not advanced under caution, and
The summing-up is impeccable and warns against treating the judge as a “13th juror”.

The Court’s insistence that “whether counsel would have raised similar questions is nothing to the point” is a crisp and important refinement: the problem is not the content of the questions in the abstract, but the identity and role of the questioner. In adversarial criminal justice, the judge must not be seen to join one side’s cause—particularly when a defendant’s credibility on a central issue is at stake.

The decision will likely be frequently cited in appeals challenging convictions on the ground of judicial interventions, and it provides pragmatic guidance to trial judges and advocates alike. Its message is simple but weighty: neutrality in form and appearance is not a mere nicety; it is a structural safeguard of a fair trial. Where that neutrality is compromised in a way that may have influenced the jury’s appraisal of the defendant’s credibility, the conviction cannot stand.