David Cameron will be propelled back into Downing Street after the general election thanks to the SNP taking seats off Labour in Scotland, according to a detailed constituency analysis.
Professor Richard Rose, director of the Centre for the Study of Public Policy at the University of Strathclyde, predicted the Tories will lose seats and Labour will make gains.
But he forecast that Ed Miliband will not be able to overhaul the Tories’ 48-seat advantage from the 2010 general election and will remain 19 behind thanks to the surge in support for the Nationalists in Scotland.
He predicted the number of SNP seats will surge from only six to 45, while Labour’s total north of the Border will collapse from 41 to ten.
Although Ukip will also experience a large increase in support, he said the way in which their vote is spread across the country will mean they pick up only four seats.
The net result would be a hung parliament with the Tories the largest party, according to the analysis. It said they could rule as a minority Government as the Liberal Democrats will only win 13 seats, too few to hold the balance of power.
Although all the other parties would together have a majority, an accompanying commentary by Savvas Savouri, Toscafund’s chief economist, predicted they would be divided and in some cases demoralised.
The SNP has indicated support for propping up a minority Ed Miliband government but he said this was more about trying to win support from former Labour voters than wanting to be a “useful accessory”
He said that in reality the Nationalists could not prop up Labour after “resoundingly trouncing” their opponents as it would be viewed as a “volte face” and undermine their re-election campaign in next year’s Scottish Parliament elections.
In his conclusion, Mr Savuori said: “When the final result is declared on Friday, May 8, David Cameron will still be in Downing Street. This is not because the electorate has given his party a big vote of confidence but because it can lose votes and seats without being overtaken by a Labour opposition that is losing seats as well as winning them.
“How far below 300 seats the Conservatives fall is less relevant than the British principle that one seat is enough to make a party a winner – at least for the time being.”
He said Mr Cameron should call a vote of confidence within ten days of the election, which, if he won, would allow him to rule for at least a year.
It would take months for Labour and the Liberal Democrats to decide on new leadership and work out a strategy for power, while he argued the SNP could be bought off with promises of extra powers beyond the Smith Commission deal.
Professor Rose’s figures are based on a constituency-by-constituency analysis of how four smaller parties – the SNP, the Lib Dems, Ukip and the Greens – will impact on the number of seats won by Labour and the Tories.
It was published as Lord Ashcroft confirmed he will publish detailed Scottish constituency polling on Wednesday.
The academic predicted a majority of seats changing hands in 2015 will involve third-force parties gaining or losing seats.
According to his analysis, the number of Tory seats will fall from 306 to 292. Although the Conservatives will lose 36 seats to Labour and four to Ukip, they will pick up 26 from the Lib Dems.
Labour will win 273 seats, according to his calculations, 15 more than in 2010. But it will lose 31 seats to the Nationalists, who are also on course to pick up eight Scottish seats from the Lib Dems.
The mismatch between seats and votes will be “extreme”, the analysis said, as Ukip can easily win up to 15 per cent of the UK vote and get less than one per cent of MPs.
The Green Party can win easily more than a million votes and get only one MP, but the SNP’s share of seats will be more than double its share of the national vote.