The chances of an SNP- Liberal Democrat coalition following the Scottish parliamentary elections on May 3 will diminish significantly today when Sir Menzies Campbell launches a withering personal attack on his Nationalist counterpart Alex Salmond.

The mocking broadside will come this afternoon on the opening day of the party's conference in Aviemore and just 48 hours after the SNP offered a sizeable olive branch to its political opponents, saying it was "optimistic" of striking a deal with the LibDems.

However, Sir Menzies will tell the party faithful: "The Nationalist leader claims Scotland's future is his highest priority but this is the same man who uses the Scottish electorate as a vehicle for his personal ambition. From Scotland to Westminster, from Westminster to Scotland, and then back again.

"He is like the Grand Old Duke of York of Scottish politics: when he was up he was up and when he was down he was down but most of the time he is half way up, which is neither up nor down."

The Fife MP will call on Mr Salmond to make up his mind and resign immediately from his Westminster seat of Banff and Buchan.

"The Nationalists," the LibDem leader will argue, "are playing politics with the Union and playing fast and loose with the future of Scotland.

"They match their rhetoric with commitments that they could never deliver because, for the SNP, the aim is not good government at Holyrood, it is populism in the pursuit of divorce from England."

The LibDems have consistently ruled out-of-hand any chance of a coalition with the Nationalists so long as they continue to insist on holding a referendum on Scottish independence. Yet, this is at the very heart of the SNP's manifesto.

Sir Menzies will again claim that election issues are being diminished by "sterile exchanges" between Nationalist rhetoric and Labour's "endless statistics".

He will insist: "The Liberal Democrats will fight this election on the basis of what matters to Scots and in the interests of Scotland. Our party has been the driving force behind radical reform in Scotland.

"Not just the achievements for which we are already known - the abolition of tuition fees, free personal care for the elderly and proportional representation for local government, but also for the detailed policies which make a real difference to Scots' lives - trebling recycling rates, investing in medical diagnostics and freeing up teachers' time so that they are able to spend more of it helping children to learn."

He will add: "In this election, we will be focusing on the issues that matter, including increasing investment in local health services, smaller class sizes and increasing police numbers."

Earlier this week, Angus Robertson, the SNP's campaign manager, underlined his party's insistence that an independence referendum was "non-negotiable".

The Moray MP claimed the overwhelming majority of Liberal Democrat members were in favour of one and stressed: "It is hardly liberal or democratic to suggest that people shouldn't have a choice in the matter."

However, he added: "The people need to speak in this election first and we take nothing for granted."