A former Labour MEP has called for an SNP vote in May because independence would amount to a "veritable impeachment" of Tony Blair over Iraq.

The call from Professor Ken Coates, chairman of the Bertrand Russell Peace Foundation, coincides with the resumption in hostilities between Lord Robertson of Port Ellen, the former secretary general of Nato, and Alex Salmond over the SNP's proposals to withdraw from the alliance.

The call from Mr Coates, an MEP for 10 years and chairman of the parliament's human rights sub-committee for half of that time, coincides with a similar intervention from CND veteran Bruce Kent, who argued that SNP victory could halt replacement of Trident.

Mr Coates wrote to Mr Salmond about Iraq, saying: "Votes in Wales and Scotland should go to Nationalist supporters, or to other groups which are willing to give their support for independence.

"If Scotland were to make a serious attempt to win a referendum for independence, this would be a veritable impeachment of the Prime Minister and those in the political classes who have supinely left him unchallenged on the essential matter."

Lord Robertson's renewed war of words with Mr Salmond harks back to his spats as shadow Scottish Secretary when he spoke of the "dark side of nationalism", and his fury when as Defence Secretary he heard Mr Salmond denounce the bombing of Belgrade during the Kosovo conflict as "unpardonable folly".

This week he writes in Holyrood magazine: "There are real tests about fitness to govern.

"Being trusted on the defence and safety of your country is one of the toughest tests a Scottish party must pass to gain the support of a wise people.

"A policy of being the first country in history to withdraw from Nato is reckless, illogical and ill-judged, and assuredly fails that critical trust test."

Mr Salmond said yesterday he did not agree with Lord Robertson about Kosovo at the time and did not agree now, given that it provided a template for illegal military intervention leading to the invasion of Iraq.

He pointed out that SNP policy was to remain in the Partnership for Peace group of countries outwith the Nato command structure, which included Finland, Sweden, Austria and Ireland.