AN SNP surge across Scotland would hand David Cameron the keys to 10 Downing Street on May 7, according to the most detailed General Election analysis to date.

In a new discussion paper, Professor Richard Rose, of Strathclyde University, predicts sweeping gains for the SNP at Labour's expense.

Combined with a strong vote for UKIP and the Greens down south, and the collapse of the Libs Dems, he suggests the final result will leave the Conservatives with about 292 seats and Labour on around 273.

As leader of the biggest party but well short of a Commons majority of 326, Mr Cameron would call a vote of confidence in a new Conservative Government within 10 days of the election, Professor Rose argues.

Under electoral law, losing a confidence vote would trigger a second election in June, unless Labour could assemble an effective government within 14 days.

However, the academic concludes: "A second -place Labour leader will find it difficult to organize an alternative government with demoralized Liberal Democrats

and an SNP that has beaten Labour badly in Scotland.

"A hung Parliament can hang for two years or more."

The report, commissioned by asset manager Toscafund, was welcomed by the SNP, which said it confirmed strong levels of support for the party.

However, it also reinforced Labour warnings that a vote for the SNP could deliver an "accidental" victory for the Conservatives.

The study predicts the SNP will win 45 of Scotland's 59 seats, up from six, as Labour's tally plummets from 41 to 10.

It says, for the first time, more Scots will view the key issue in a Westminster election as "which party can do best for Scotland?"

As a result, the Nationalists pose a "categorical" threat to Labour, as they are placed to draw support from the 45 per cent of Scots who backed independence last year while the 55 per cent No vote will be split between several parties.

It says "the surge in SNP support creates a barrier to Labour gaining more than 280 seats" while "the swings and roundabouts of constituency competition" keep the Tories below 300.

However, it is Professor Rose's assessment of what will happen in the aftermath of the election that will prove most controversial.

He argues Mr Cameron will win a confidence vote "by default" because Labour will be unable to win the backing of smaller parties, including the SNP.

He says: "A Labour attempt to lead some sort of coalition government would face sceptical potential partners. "After suffering a major

defeat, the Liberal Democrats would not have a leader who could represent the party in negotiations with Labour and MPs who had survived the party's electoral debacle would likely be shy of another coalition.

"A triumphant SNP could well have sufficient seats to put Labour in office, but to do so after resoundingly trouncing Labour in Scotland would be a volte face.

"Equally important, it would undermine the SNP's campaign to remain the Scottish government in competition with Labour at

the May, 2016 Scottish Parliament election.

"The friendly noises that SNP leaders are making about Labour policies are part

of a campaign to gain support from ex-Labour voters in Scottish constituencies rather than expressing a wish to be seen as a useful accessory to a Labour government at Westminster."

Prof Rose, one of the UK's leading elections experts, argues it would be "logical" for the SNP not to vote against a Conservative government provided it won major concessions on devolving powers to Holyrood - a central part of the Nationalists campaign.

The SNP would also welcome the prospect of an in/out referendum on Britain's EU membership in 2017, as promised by Mr Cameron, as the party believes it could trigger a second independence poll, he argues.

The conclusion contradicts reassurances from First Minister Nicola Sturgeon that the SNP would not prop up a minority Tory government.