Nick Clegg today urges Tory and Labour supporters to put aside their traditional allegiances and lend their votes to the Liberal Democrats in a bid to stop the SNP surge producing a near wipe-out for his party in Scotland.

The Deputy Prime Minister, who will visit Gordon where the Lib Dem candidate Christine Jardine is trying to retain the seat - held for many years by her party colleague Sir Malcolm Bruce - for the Lib Dems against the bid from Alex Salmond to take it. He will insist only his party can keep the former SNP leader and ex-First Minister out of the House of Commons.

With Mr Clegg's party polling as low as two per cent in Scotland and several incumbents like Danny Alexander, Michael Moore and Jo Swinson facing stiff challenges from the Nationalists, the DPM will launch a broadside against Nicola Sturgeon's party, saying: "They are not the party of Scotland, they are the party of debt."

On the campaign trail, he will tell voters: "In 11 Scottish seats, you face a simple choice: do you want an SNP MP or a Liberal Democrat MP?

"In these seats the Liberal Democrat candidate is the only one that is in a position to beat the SNP. So if you are someone who is considering voting for the Conservative or Labour candidate, my message to you is this: lend us your vote and we can stop the SNP winning in your constituency."

After warning of the possibility of Ukip leader Nigel Farage propping up David Cameron, Mr Clegg will claim the SNP would keep a minority Labour administration "on life support" while the Nationalists plotted a fresh bid for independence.

"Do you really want a government on life support, with Alex Salmond deciding whether it succeeds or dies?" he will ask.

The DPM will also attack the SNP's economic policies, saying: "The SNP are not the party of Scotland, they are the party of debt. They want to borrow more and more money - an eye-watering £180bn - and their plans for full fiscal autonomy will cost the people of Scotland £7.6bn.

"They will risk our economy and leave our children and grandchildren to pay for it for years to come. The Liberal Democrats are working for Scotland in a way that is responsible, fair and keeps the country on track," he will add.

Earlier, the Lib Dem leader warned of the "blukip" threat in which Mr Cameron would be held to ransom by a right-wing cabal of Ukip, the DUP and his own right-wing backbenchers.

"There is a Right wing threat to Britain," he declared, adding: "The only way to stop it is to make sure there are enough Liberal Democrat MPs to keep the next government anchored in the centre ground."