‘I told Alex I hoped this was not how they would go on’

not to say anything until he had made new appointments.

Lord Steel said: “The reason I relinquished the role was that I was appalled by the language being used by Alex Salmond, [justice secretary] Kenny MacAskill and an authorised spokesman towards the judiciary on the Supreme Court and the Secretary of State.

“I told Alex that I hoped this was not the way they were going to continue now that they had an overall majority, because, if so, I expected a growing number of complaints against ministers.

“Whether my letter had any effect I do not know.

“He sent me a polite and effusive letter of thanks for my services, but I am glad to observe that there has been no repetition of attacking the messengers instead of arguing the message.”

The constitutional argument was triggered in May after a series of rulings by the Supreme Court on Scottish criminal law.

At the time, Mr Salmond sought to defend the historic independence of the Scottish legal system, saying the Supreme Court should have no role.

But he went on to accuse Lord Hope, one of the Supreme Court’s Scottish judges, of making “wrong-headed” decisions in human rights cases.

At the time, Mr MacAskill said the Supreme Court judges’ knowledge of Scots law came from what they picked up on a trip to the Edinburgh Festival and made veiled threats to withdraw their funding, after the London-based court effectively quashed Nat Fraser’s conviction – for killing his wife – on human rights grounds.

The attacks prompted a row, with claims that the Scottish Government was exerting undue influence on the judiciary.

Lord Steel and George Reid, also a former presiding officer, will be replaced by former Lord Advocates Dame Elish Angiolini and Lord Peter Fraser. Mr Reid said he was quitting after being appointed the Queen’s Lord Lieutenant in Clackmannanshire.

Scottish Conservative deputy leader Murdo Fraser said: “This is an extraordinary broadside from Lord Steel.

“The First Minister is fond of shooting from the lip and living in a world where he believes he is always right. This should serve as a wake-up call.”

Scottish Lib Dem leader Willie Rennie said: “I am not surprised David Steel feels this way. He knows it is important to keep the judiciary separate from politics. SNP ministers put that at risk.”

Labour leader Iain Gray said: “This is a damning indictment, not of SNP policy but Alex Salmond’s lack of judgment.”

A spokesman for the Scottish Government said: “The First Minister is extremely grateful to Lord Steel for his service as an independent adviser to the Ministerial Code for three years, and we wish him extremely well for the future.”