SCOTLAND'S top prosecutor has been accused of failing to fulfil his duties under human rights legislation in a landmark hearing about whether a disabled grandfather can receive help ending his life.

Aidan O'Neill QC, who represented 66-year-old Gordon Ross in the Court of Session, said the Lord Advocate was "obfuscating" and "avoiding the question" of how someone who assisted a suicide would be treated by the law.

But during the intense exchange Gerry Moynihan QC said the Lord Advocate's policy was "crystal clear" and later summed it up "in a nutshell" with the words "he will prosecute".

Mr Ross suffers from severe Parkinson's disease and can no longer walk, dress or feed himself. Every day he endures painful episodes of violent shaking and his condition has deteriorated so much he was unable to travel from his Glasgow care home to Edinburgh for the hearing.

Two of his four children, Jon and Veronica Ross, along with his former wife Sheila Barclay joined a group of almost 30 supporters outside the court holding placards which read "Support Gordon's choice".

Ms Ross said: "I feel very proud of my dad. I understand why he is doing it because the disease is a horrible thing and whilst he is doing very well and being very brave dealing with it just now, it is going to get worse."

Mr Ross, a former TV producer, and his family insist he is not currently suicidal. He launched his case to call on the Lord Advocate to issue guidance clarifying whether anyone who helped him die in the future would be charged with an offence.

Such guidelines have been published by the Director of Public Prosecutions (DPP) in England but do not apply in Scotland.

Opening the case, Mr O'Neill QC argued that the Lord Advocate's failure to identify the facts and circumstances he would take into account when deciding to prosecute someone who assisted in a suicide was incompatible with the European Convention on Human Rights (ECHR).

He called on the court to order the Lord Advocate to outline his policy - as the House of Lords did in England following a case taken by multiple sclerosis sufferer Debbie Purdy.

The only clarity being offered by the Lord Advocate was that he "cannot conceive of circumstances when he would not prosecute," said Mr O'Neill, adding: "That is not clarity, that is just unlawful."

He clashed with Mr Moynihan over what was required by the ECHR. Mr Moynihan said the ECHR "does not establish a substantive right to assisted suicide - quite the opposite. It leaves that to domestic law."

They also disagreed on the relevance of the Purdy case to Scotland and Mr Moynihan indicated the DPP guidelines still left uncertainty about how individual cases of assisted suicide would be seen by the law. He said: "Unless Mr Ross were to articulate a precise list of circumstances I would not even know that he would be free to do in England what he is not free to do here."

Judge Lord Doherty described the case as "interesting and important" before the court rose. A ruling is expected in around six weeks.

Jon Ross said he hoped his father had as much time as possible before he took any decision on ending his life, but also wanted him "to be able to have that decision."

In a statement Dr Gordon Macdonald, of Care Not Killing - the umbrella group against legalising assisted suicide in Scotland, said: "Care Not Killing believes that legalising assisted suicide changes the culture surrounding care for sick and dying people, and would be a catastrophe in terms of how our society confronts illness and disability - not to mention devaluing suicide prevention efforts.

"Proposed so-called safeguards assume that those who will request assisted suicide will know their own minds beyond doubt. This is a false assumption.

"In today's individualistic society the pressures on sick, disabled and elderly people to avoid placing 'unfair burdens' on others are very great.

"Maintaining the law's protection of this silent and vulnerable majority is more important than giving choices to a minority of strong-minded and highly resolute people."