The “unusual” argument was made in the case of Michael McDonald, 56, an alcoholic who murdered his ex-girlfriend Breda Cummins, 31, in Athy, Co Kildare on 13 May 2010.

Mr McDonald had been in a five-year relationship with Ms Cummins which ended six weeks earlier. He admitting killing his ex-partner by stabbing her six times to the chest as she lay in bed, but denied it was murder.

The defence at trial was that Mr McDonald’s responsibility was diminished due to schizoaffective disorder. The jury rejected the argument and found him guilty of murder. He was accordingly given the mandatory life sentence by Ms Justice Iseult O’Malley on 23 November 2012.

Moving to appeal his conviction yesterday, Mr McDonald’s barrister, Michael Lynn SC, submitted that the jury ought to have been allowed to consider whether Mr McDonald’s alcoholism, or alcohol dependence syndrome, diminished his responsibility for murder.

Mr Lynn said two psychiatric experts, for both the prosecution and defence, agreed that Mr McDonald suffered from alcoholism or alcohol dependence syndrome. However, both experts also agreed that the condition did not fall within the definition of the Criminal Justice (Insanity) Act 2006 for diminished responsibility.

It was an “erroneous consensus” that alcoholism could not apply to the defence of diminished responsibility, Mr Lynn contended. It deprived Mr McDonald of the chance to run a “significant defence” and resulted in a “fundamental injustice”.

Mr Lynn submitted that alcoholism can be regarded as a “disease of the mind” coming within the definition of the statute. While the 2006 Act excludes intoxication as a factor for diminished responsibility, it did not mean alcoholism or alcohol dependence syndrome, was excluded. It was a legal question on the interpretation of the statue, he added.

Counsel said the actual long-term affects of alcohol dependence syndrome may not have been properly explored by the doctors due to the “erroneous consensus” that it couldn’t apply to diminished responsibility. If there was a “collective misunderstanding” on the effects of alcoholism, then Mr McDonald suffered an injustice, Mr Lynn submitted.

Orla Crowe SC, counsel for the Director of Public Prosecutions, said the trial was being criticised for matters that did not emerge on the evidence. There was no evidence, she said, that alcohol dependent syndrome played a part in the murder other than that it was something Mr McDonald suffered from.

Ms Crowe said both experts agreed that Mr McDonald had alcohol dependent syndrome but both experts also agreed that it did not come within the definition of the statue. She said the defence’s own psychiatric expert was of the view that this was not “an intoxication-driven event”.

The same expert advanced the view that Mr McDonald had schizoaffective disorder which affected his ability to make logical and rational judgments over time, but the jury rejected the claim that it diminished his responsibility for murder, according to Ms Crowe.

She said the Court of Appeal was being asked to speculate and to ignore the experts’ opinions seven years after a properly-conducted trial.

Mr Justice George Birmingham, president of the Court of Appeal, who sat with Mr Justice Patrick McCarthy and Ms Justice Isobel Kennedy, said the court would reserve its judgment to consider the “unusual” argument.

Mr Justice Birmingham commented earlier that it was an “interesting argument”, perhaps an “academic argument”, but it did not seem to be grounded on the facts of the case.

Ruaidhrí Giblin, Ireland International News Agency Ltd.