Self-Defence and the Reliability of Expert Evidence
| Published date | 01 December 2024 |
| DOI | http://doi.org/10.1177/00220183241292460 |
| Author | Tony Ward |
| Date | 01 December 2024 |
Self-Defence and the Reliability
of Expert Evidence
R v Mazzer [2024] EWCA Crim 557
Keywords
Self-defence, expert evidence, reliability, PTSD
The applicant was convicted on two counts of causing GBH with intent and sentenced to concurrent terms
of 42 months’imprisonment. He had stabbed two young men during a confrontation between a group of
pupils from his school, who were attending a party, and a group from another school who came to the
house where the party was held but were not let in. The defence was that he had acted in self-defence.
He had taken a knife from the kitchen in a state of panic, having been seriously injured in a previous inci-
dent involving boys from the other school. He described being punched, kicked and scratched –which
was disputed –and waving the knife around to deter his attackers, without any intention of causing
serious injury.
After conviction, the applicant was examined by a psychologist, Professor Farrell, who reported that
he was suffering from PTSD as a result of the earlier incident. The report was taken into account as a
mitigating factor in sentencing but the applicant applied for leave to introduce it as fresh evidence for
the purpose of an appeal against conviction.
Professor Farrell’s report stated: ‘An existing condition of PTSD would, in strong likelihood, result in
miscalculation of threat level, appraisal of current situation, a more heightened perception of threat, which
can result in more extreme reactions and engagement in safety behaviour’.
Held, refusing the application: evidence of PTSD could be relevant in a case of self-defence, both to
the question of what threat the defendant honestly believed he faced, and to the level of force he believed
was necessary, which was relevant though not decisive factor in assessing the reasonableness of the force
used (R v Thompson [2013] EWCA Crim 1849 followed).
The evidence must, however, be ‘sufficiently reliable to be admitted’(Criminal Practice Direction
(CPD) 2023 [7.1.1]). In this context it was usually necessary for the expert’s report to be tethered to
the evidence about the events, and in particular, any account given by the defendant; otherwise, it was
likely only to confuse a jury. It was unlikely to be helpful for a psychiatrist or a psychologist to give
general evidence diagnosing a condition in a defendant and saying what its effects might have been
without also saying how, in the opinion of the expert, that related to the accounts given by the defendant,
and by any relevant witnesses, as to what took place. The report must also set out the expert’s reasons for
the opinions given (R v Jacobs [2024] 4 WLR 8 considered).
Professor Farrell’s opinion was not tethered to the evidence in this way. It did not say how any
particular circumstance could have been viewed differently by the applicant because of PTSD and
hypervigilance. It did not even deal with Mazzer’s taking a knife from the kitchen drawer. The
defence at trial had not been that the defendant miscalculated the threat he faced, but that he had been
punched and kicked and used reasonable force to defend himself. It was for the jury to decide
Case Note
The Journal of Criminal Law
2024, Vol. 88(5-6) 398–400
© The Author(s) 2024
Article reuse guidelines:
sagepub.com/journals-permissions
DOI: 10.1177/00220183241292460
journals.sagepub.com/home/clj
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