SNP policies have placed a bomb under the party that will undermine its long-term prospects of electoral success in Scotland, according to Sir Malcolm Rifkind.

The former Scottish Secretary, who has recently published his memoirs Power and Pragmatism, said he believed voters in parts of Scotland where Conservative support has been strongest such as Galloway, Perthshire and the north-east would increasingly feel unable to support the SNP.

“There will come a point when large numbers of Scots get fed-up with it,” he said. Sir Malcolm was Scottish secretary under Margaret Thatcher, and later foreign secretary under John Major. He lost his Pentlands seat in Edinburgh in the Tory wipeout of 1997.

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He puts the recent recovery of support for the Scottish Conservatives partly down to their leader Ruth Davidson. Under her leadership, the Tories have staged an electoral recovery, clinching 31 seats at the recent Holyrood elections, a 16-seat leap since 2011.

The party secured about 22 per cent of the popular vote, but still polled less than it managed under John Major in 1992.

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By finishing second behind the SNP, it became Holyrood’s official opposition, but remains slightly behind Scottish Labour in the share of the vote. Scottish Labour secured 22.6 per cent of votes.

Sir Malcolm said: “By very good fortune, the Tory party is being led by someone who Scots identify with as being a normal, home-grown member of the human race. She’s one of us.”

He said Ms Davidson’s success combined with the SNP’s policies meant the Tories would continue to recover while the SNP slides. The Nationalists, he said, had become the most left-wing party in Scotland, but that could not continue indefinitely.

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“They’re anti-austerity, they’re anti-Trident and pretty much on every other trendy issue they go for the left-wing view,” he said.

“But in Perthshire, in Galloway, in the north-east of Scotland and elsewhere, people are not prepared to see themselves, not just as left wing, but pretty hard left.”

Speaking in an interview with The Herald Magazine published today, Sir Malcolm, who retired from the Commons last year after he was accused of taking “cash for access”, said the policies amounted to a political bomb under the SNP.

“And it’s already begun to tick,” he said. “What we saw at the last election wasn’t just that the Tories won votes, they won back votes they’d lost to the SNP and that process has begun.

HeraldScotland: LONDON, ENGLAND - FEBRUARY 23:  Sir Malcolm Rifkind walks to his home from Parliament on February 23, 2015 in London, England. Former Conservative Foreign Secretary Rifkin and Jack Straw, a former Foreign Secretary in the last Labour government have been

“I’m not saying it’s 100 per cent certain it will continue, but what the last Scottish election showed is the public, if the Tories get their act right, no longer say, ‘We will never vote Conservative’.”

Sir Malcolm also said he believed the political circumstances in Scotland meant that another referendum on independence would not happen because the First Minister knows she would lose it.

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“Not only is it a complete try on but I don’t think Nicola Sturgeon herself wants one because she knows she would lose and if the opinion polls are to be believed, they would lose.”

Sir Malcolm said the lack of clarity on the currency, the collapse of the oil price and the potential of Brexit and independence creating a hard border between Scotland and England all made the referendum unlikely.