Expert Witness Journal Issue 65 February 2026 - Flipbook - Page 65
Supreme Court ruling:
Illegality defence applies despite
insanity acquittal
by Owen Fear, Senior Associate & Katie Viggers, Professional Development Lawyer
at Browne Jacobson
The Supreme Court has unanimously ruled that a
man found not guilty of murder by reason of insanity
cannot pursue civil claims in negligence to recover
compensation for the consequences of his killings,
applying the doctrine of illegality to bar his claim.
hospital, preventing the killings of the three men.
He sought damages for the consequences of the
killings, including his compulsory detention, and an
indemnity against potential claims from the victims’
families.
The case –
Lewis-Ranwell v G4S Health Services (UK)
Ltd and others [2026] UKSC 2
The legal issue
The central question was whether the doctrine
of illegality – which prevents individuals from
pro昀椀ting from their own wrongdoing – barred Mr
Lewis-Ranwell’s civil claim in negligence3, despite
his lack of criminal responsibility.
Mr Lewis-Ranwell, who had been diagnosed with
schizophrenia, attacked and killed three elderly
men in their homes on 10 February 2019. At the time,
he was experiencing a serious psychotic episode
and held the delusional belief that his victims were
paedophiles.
The Supreme Court’s decision
The Supreme Court held that the illegality defence
applied in the circumstances and that Mr LewisRanwell was barred from bringing civil proceedings
in negligence, even though there was no criminal
conviction. The Court rejected the argument that
the distinction between diminished responsibility (a
partial defence reducing murder to manslaughter)
and insanity (a complete defence) should determine
the availability of the illegality defence in civil law.
Following his arrest, Mr Lewis-Ranwell was tried for
murder but found not guilty by reason of insanity,
meaning the jury accepted he carried out the
killings but was not criminally responsible. He was
detained at Broadmoor Hospital under a hospital
order with restrictions, where he remains.
The negligence claim
Key principles
Mr Lewis-Ranwell brought civil proceedings
against four defendants1 – G4S Health Services
(UK) Limited, the Chief Constable of Devon and
Cornwall Police, Devon Partnership NHS Trust,
and Devon County Council. He alleged that they
were all negligent in failing to provide him with
adequate mental health care or assessment2 in the
days before the killings. He had been arrested twice
shortly before the murders for suspected burglary
and assault, and during both detentions, he behaved
erratically and appeared severely mentally unwell.
He was seen by mental health practitioners and the
need for a mental health assessment was discussed
but not arranged before he was released on bail.
The threshold question
The Court 昀椀rst considered whether the act in
question – the killing of three men – constituted
unlawful conduct serious enough to engage the
illegality defence. A threshold is needed because it
would be unjust if trivial acts of unlawfulness barred
otherwise valid legal claims. The acts must engage
the public interest, but the claimant’s actions do not
have to carry criminal responsibility to cross the
threshold.
Was the defence of illegality engaged in this case?
The Supreme Court held that, even though there
was no 昀椀nding of criminal responsibility, the jury’s
verdict established that Mr Lewis-Ranwell did kill the
Mr Lewis-Ranwell alleged that, but for the alleged
negligence, he would have been admitted to
EXPERT WITNESS JOURNAL
63
FEBRUARY 2026
