Ratio Decidendi
For the partial defence of diminished responsibility under s 52 Coroners and Justice Act 2009, 'substantial' impairment means an impairment that is more than merely trivial — it need not be total but it must be significant or appreciable.
Facts
The defendant killed his partner. He raised the partial defence of diminished responsibility, relying on a personality disorder.
Judgment Summary
The Supreme Court held that 'substantial' means something between trivial and total. In most cases, no direction is needed on the meaning of substantial, but where there is an issue, the judge should direct that it means more than merely trivial.
Key Quotes
"Substantial does not mean total, but it means more than merely trivial or minimal."
— Lord Hughes
Subsequent Treatment
The leading authority on the meaning of 'substantial' in the diminished responsibility defence.