The SNP will help make Ed Miliband Prime Minister even if Labour finish 40 seats behind the Tories at the general election, Nicola Sturgeon said last night. The Scottish First Minister said she would form an anti-Tory alliance with Labour and other smaller parties regardless of how many MPs David Cameron wins on May 7. While Mr Miliband has ruled out going into coalition with the SNP, Ms Sturgeon's remarks raise the prospect of Labour ruling as a minority government - despite winning fewer votes and seats than the Tories. Protesters wearing masks of SNP leader Nicola Sturgeon hold placards outside Chatham House, a foreign affairs think-tank, where Labour leader Ed Miliband delivered a speech in London this morning . The SNP could win as many as 50 MPs in Scotland - allowing Mr Miliband to become Prime Minister even if he falls far short of a majority. Her comments came as Labour slipped four points behind the Tories in the latest polls - with David Cameron's Tories moving to 36 per cent. However, the SNP could win as many as 50 MPs in Scotland - allowing Mr Miliband to become Prime Minister even if he falls far short of a majority. Ms Sturgeon was asked on BBC2's Newsnight whether her party would be ready to prop up a Labour government if the party had fewer seats than the Conservatives. She replied: ' Yes. Even if the Tories are the largest party, if there is an anti Tory majority, my offer to Labour is to work together to keep the Tories out.' Asked if this would remain her position even if Mr Cameron had 30 more MPs than Mr Miliband, she confirmed: ' If there is an anti Tory majority, yes, that's what I've been saying all along - I'm not sure why there's any confusion about it - that we would work with Labour to stop the Tories getting into Downing Street.' And if the margin was as wide as 40 MPs, she said: ' If they can't command a majority they can't be a government, that's the basic rule of how governments are formed I'd have thought.' The SNP leader Nicola Sturgeon - campaigning in Glasgow today - said she would help make Ed Miliband Prime Minister even if Labour finish 40 seats behind the Tories . Ms Sturgeon was pictured with three-year-old Kitty MacDonald and SNP Candidate for Glasgow South Stewart McDonald during a visit to Glazed, a ceramic painting studio in the city . Ms Sturgeon also rejected an independent study which said there was a 'significant disconnect' between the SNP's claims to be an anti-austerity party and plans that implied it would be spending less than Labour by 2019/20. The Institute for Fiscal Studies accused  the major parties of keeping voters 'in the dark' by spelling out only the 'broad outlines' of their tax and spend plans following the May 7 poll, though it  singled out the Liberal Democrats for being more transparent than their rivals about their intentions. Ed Miliband, pictured in Chatham House, central London today, could become Prime Minister even if he wins fewer votes and MPs than David Cameron . The thinktank's deputy director Carl Emmerson said: 'There are genuinely big differences between the main parties' fiscal plans. 'The electorate has a real choice, although it can at best see only the broad outlines of that choice.' Conservatives say they would eliminate the deficit by 2017/18 and start to run a surplus while Labour says it will reduce the deficit each year and balance the books 'as soon as possible' during the five-year term. The IFS said the Tory plans were 'predicated on substantial and almost entirely unspecified spending cuts and tax increases', and could involve 'further real cuts to unprotected departments of around £30 billion'. Labour's plans were consistent with a pledge not to borrow for day-to-day spending but 'would leave borrowing at £26 billion a year in today's terms', it said. The IFS said the Liberal Democrats had been more transparent about overall fiscal plans to 2017-18, revealing that they are aiming for tightening more than Labour but less than the Conservatives. While the SNP would 'cut less to start with', the implication of the plans spelt out in their manifesto would be that the 'period of austerity would be longer than under the other three parties we consider', it said. Responding to the comments, Liberal Democrat leader Nick Clegg said Ms Sturgeon was going to 'ignore the will of the people', if she chose to support the smaller of the two main parties at Westminster. He added: 'She's going to ignore how people vote and she's just going to insist on her personal preference.' She told the BBC's Newsnight that 'if [the Conservatives] can't command a majority, they can't be a government'. Ms Sturgeon has repeatedly said she would work with Labour to 'get rid of the Tories' if the SNP had enough MPs. The Prime Minister, speaking in Lincoln with the Foreign Secretary William Hague, has called that prospect on an SNP-Labour alliance 'frightening' and claimed it would lead to 'economic ruin' Conservative leader David Cameron has called that prospect 'frightening' and said it would lead to 'economic ruin'. While the SNP had only six MPs at Westminster in the last Parliament, recent polls suggest they could win the majority of Scotland's 59 seats. That could leave the party holding the balance of power if the election resulted in a hung parliament.
SNP leader vowed to prop up Labour even if the Tories finish clear winners .
It means Mr Miliband could be PM with fewer votes and MPs than the Tories .
He would by PM of a minority Labour government kept in power by the SNP .
Mr Miliband has ruled at a formal coalition with the Scottish nationalists .
But he has refused to rule out working with the SNP vote by vote .