SCOTLAND's most senior prosecutor has denied academic claims of a "shameful lack of clarity" on assisted suicide law.

Lord Advocate Frank Mulholland insisted that "help-to-die" would be prosecuted as homicides until such time as MSPs in Holyrood decided otherwise.

Mr Mulholland had come under pressure to provide guidance on how anyone who helps a loved one to die will be treated by the law.

Legal experts and campaigners said this week such guidance has been set out in England and accused the Crown Office of avoiding the issue north of the border.

One, Professor James Chalmers of Glasgow University, argued that the law of causation was unclear in Scotland and that, therefore, so too was the law on assisted suicide.

Mr Chalmers said it was not clear who ultimately caused a death in Scots Law - the person, who, for example, provided a pill, or the person who swallowed it.

However, writing in today's Herald, Mr Mulholland insisted the position was perfectly clear.

The Lord Advocate wrote: "Prof Chalmers raised the issue of causation. The law relating to this is clear.

"In order for there to be a sufficient causal connection for homicide the conduct must be a significant contributory factor to the death.

"A minimal or negligible contribution would not suffice.

"This clear test, which has persisted for many years, will be applied to the facts and circumstances of each case."

Mr Mulholland said that where there was sufficient credible and reliable evidence a prosecution would be in the public interest.

He added what he called "the obvious point" that homicide was such a serious crime that "it is difficult to conceive of a case where it would not be in the public interest to take proceedings".

He wrote: "But each case would be considered on its own facts and circumstances."

The Crown has resisted laying down prosecutorial guidelines. It is currently facing a legal action from a 65-year-old Glasgow grandfather, Gordon Ross, who wants to know someone could assist his death and not face criminal charges.

That legal action is at an early stage but Mr Ross has vowed to go all the way to the UK Supreme Court to establish prosecutorial guidelines.

In his letter, however, Mr Mulholland, stressed that he thought any change in the law was for parliament and not the Crown Office.

He said: "In a democracy it is important that changes to the law of assisted suicide are decided by the Scottish Parliament and not by me in the issue of prosecutorial guidance.

"Prosecutorial guidance cannot change the law or remedy a defective law. That would be unconstitutional and an affront to the rule of law.

"If members of the public want the law of this country relating to assisted suicide changed they need to persuade a majority of MSPs to do this."

Mr Chalmers had cited legal cases in Scotland where drug dealers were accused of homicide by providing substances to people who later died. Causation, he said, in such cases was unclear.

The professor said he believed this had to be addressed, either by prosecutorial guidelines or parliament. He said: "The Lord Advocate has previously issued guidance in cases where the law is unclear.

"There is nothing improper about that. Alternatively, he can himself call for reform, as he did earlier this year in relation to contempt of court."