The partial defence of diminished responsibility2was radically altered by
s. 52 of the Coroners and Justice Act 2009,3and fundamental reformula-
tions became effective on 4 October 2010.4The new provision was
designed to align the mitigating doctrine with ‘developments in diag-
nostic practice’.5To raise the revised plea successfully, the defendant
must now prove, on the balance of probabilities,6that at the time of the
killing he was suffering from an ‘abnormality of mental functioning’
arising from a ‘recognised medical condition’.7This deﬁnitional change
‘may have more far-reaching consequences than initially anticipated’.8
The Royal College of Psychiatrists considered that the ‘recognised med-
ical condition’ requirement would ‘encourage reference within expert
evidence to diagnosis in terms of one or two of the accepted internation-
ally classiﬁcatory systems of mental disorders (WHO ICD10 and AMA
DSM)’.9Both the WHO ICD10 and AMA DSM identify several different
mental and behavioural disorders arising from psychoactive substance
2 To raise the concessionary defence successfully under the old law the defendant
must have been able to prove, on the balance of probabilities, that he was
suffering from ‘such abnormality of mind (whether arising from a condition of
arrested or retarded development of mind or any inherent causes or induced by
disease or injury) as substantially impaired [D’s] mental responsibility for his acts
and omissions in doing or being a party to the killing’ (Homicide Act 1957, s. 2).
3 R. Mackay, ‘The Coroners and Justice Act 2009—Partial Defences to Murder (2)
The New Diminished Responsibility Plea’  Crim LR 290. See also R. Mackay
and B. Mitchell, ‘Loss of Control and Diminished Responsibility: Monitoring the
New Partial Defences’ (2011) 3 Archbold Review 5; C. Withey, ‘Loss of Control’
(2010) Criminal Law and Justice Weekly, 3 April 2010, available at: http://www.
criminallawandjustice.co.uk/index.php?/Analysis/loss-of-control.html, accessed 29
November 2011; Rudi Fortson QC, ‘Homicide Reforms under the CAJA 2009’,
Criminal Bar Association of England and Wales Seminar, October 2010, available
16thOct2010_R_Fortson_submitted_v.7.pdf, accessed 29 March 2011; L. Kenneﬁck,
‘Introducing a New Diminished Responsibility Defence for England and Wales’
(2011) 74 MLR 750. See generally, R v Inglis (2011) 75 JCL 105, commentary by
P. Dargue, ‘Court of Appeal: Mercy Killers and the Sentencing Rules—An Uneasy
Fit?’; H. Howard and M. Bowen, ‘Unﬁtness to Plead and the Overlap with Doli
Incapax: An Examination of the Law Commission’s Proposals for a New Capacity
Test’ (2011) 75 JCL 380.
4 Subsections (1), (1A) and (1B) of s. 2 of the Homicide Act 1957 were substituted
and inserted by s. 52(1) of the Coroners and Justice Act 2009 (see the Coroners
and Justice Act 2009 (Commencement No. 4, Transitional and Saving Provisions)
Order 2010 (SI 2010 No. 816), art. 5.
5 Ministry of Justice, Murder, Manslaughter and Infanticide, MoJ CP 19 (2008) para.
6 Placing the burden of proof on the defendant is not incompatible with the
European Convention on Human Rights, Art. 6(2); R v Lambert, Ali and Jordan
 QB 1112. See also Lilburn (David) v HM Advocate  HCJAC 41 and
C. Shead, ‘Diminished Responsibility and the Burden of Proof’ (2010) Scottish
Criminal Law 819.
7 Homicide Act 1957, s. 2, as amended by the Coroners and Justice Act 2009, s. 52.
It has been suggested that this element of the partial defence is ‘representative of a
marked shift towards medicalization of this area of the law’; Kenneﬁck, above n. 3
at 765. See also, S. Morse, Law and Psychiatry: Rethinking the Relationship
(Cambridge University Press: Cambridge, 1984).
8 Kenneﬁck, above n. 3 at 757.
9 Law Commission, Murder, Manslaughter and Infanticide, Law Com. Report No. 304
(2006) para. 5.114. See also Kenneﬁck, above n. 3 at 757.
The Journal of Criminal Law