Britain will be saddled with a crippling extra £148billion of debt if the SNP wins a share of power , the Treasury warned last night . The official costing of Nicola Sturgeon 's plans reveals they involve a massive spending spree that would have to be funded by higher taxes or even higher borrowing . The analysis , conducted by Treasury officials and signed off by the Permanent Secretary , show that spending under the SNP would be £148billion higher than forecast in this month 's Budget . It came as Gordon Brown used his valedictory speech in the Commons to warn that the 'fragile ' UK is 'potentially at a point of departure ' in the wake of last year 's referendum on Scottish independence . Scroll down for video . Nicola Sturgeon and Alex Salmond 's plans for a deal with Labour could cost Britain £148billion . The Conservatives seized on the Treasury figures as evidence that a Labour government propped up by the SNP would force Britain deeper into the red . A spokesman said taxpayers would be landed with a huge bill if the parties ended up in power . 'It is now impossible for Ed Miliband to become Prime Minister without crawling into Downing Street on the coat tails of the SNP – with Alex Salmond calling the tune , ' he said . 'We now know the consequence of that will be £148billion more borrowing , higher taxes , unlimited welfare , and weaker defence . ' David Cameron this week branded Ed Miliband ( pictured ) 'Alex Salmond 's poodle' – warning that Labour would be forced to dance to the SNP 's tune . Miss Sturgeon , the SNP 's leader , has pledged to reverse austerity measures if she wins a share of power in May . While the Conservatives are promising to identify £30billion of spending and welfare cuts , Miss Sturgeon says she would increase real-terms public spending by at least half a per cent a year to allow extra 'investment ' . The Treasury analysis suggests this would lead to massive additional spending , adding to Britain 's £1.5trillion debt mountain . It suggests the SNP 's plans would involve an extra £20.7billion spending next year , an extra £39.7billion in 2017-18 , an extra £48.8billion in 2018-19 and an extra £38.3billion in 2019-20 . The analysis is a blow to the SNP , whose economic credibility is already under question , but it is also a setback for Labour , which may be forced to do a deal with the nationalists who appear poised to claim dozens of Labour seats at the election . Former SNP leader Mr Salmond , who hopes to return to Westminster as kingmaker , says his party will vote down any attempt by the Tories to run a minority government after the election . Instead , he says his MPs will line up with Labour to put Mr Miliband in Downing Street . David Cameron this week branded Mr Miliband 'Alex Salmond 's poodle ' – warning that Labour would be forced to dance to the SNP 's tune . The SNP 's plans were facing fresh scrutiny last night over claims that the party 'fiddled the figures ' in order to hide a £4.1billion hole in its bid for Scotland to be handed full economic powers . Labour called for an inquiry into the proposals , amid fears the collapse in the price of oil makes them unsustainable . A study by leading economist Professor Brian Ashcroft and the Scottish Parliament Information Centre , found that the plans now fell more than £4billion short . Labour 's deputy leader in Scotland Kezia Dugdale said the report left the SNP 's plans 'in tatters ' . But Miss Sturgeon dismissed the report , saying that taking full control of economic powers was the only way to 'defend ' Scotland from Westminster cuts .
Nicola Sturgeon 's plans for deal with Labour could cost Britain £148billion . Massive spending spree would be funded by higher taxes or borrowing . Tories said taxpayers would be landed with huge bill if parties win power . But SNP says it will not raise income tax and is committed to keeping public services free at the point of use.