Nicola Sturgeon yesterday vowed to work with Labour to ‘ lock the Tories out ’ of power . In an extraordinary speech in London , Scotland ’ s first minister claimed voters across the UK would welcome her party ’ s influence at Westminster , saying she would end austerity . But , following mounting pressure from senior colleagues , Ed Miliband last night tried to draw a line under speculation about a Labour-SNP government by ruling out a formal coalition . Labour leader Ed Miliband said a formal coalition with the SNP 'will not happen ' - but failed to rule out forming a looser alliance on a vote-by-vote basis . The Labour leader said there would be ‘ no SNP ministers ’ in any government he leads after May ’ s general election . But Mr Miliband pointedly refused to rule out a deal that would see the resurgent Scottish nationalists prop up a minority Labour government in key Commons votes – the preferred option of Miss Sturgeon . ‘ This was a lot of hype to rule out something no one was proposing , ’ the first minister said . ‘ Mr Miliband ’ s statement is absolutely fine from our point of view , because formal coalition with seats in the UK government has never been our preference . ‘ But working with Labour in a looser arrangement , I certainly wouldn ’ t rule out because I want to see SNP MPs in the House of Commons pushing for progressive change . I also don ’ t want to see David Cameron re-elected . 'As long as there are more SNP and Labour MPs than there are Tory MPs , we can lock the Tories out of government , there is no question about that. ’ Pollsters suggest the SNP is on course for an unprecedented breakthrough at the general election , winning dozens of Labour seats and depriving Mr Miliband of any chance of a majority . John Curtice , of Strathclyde University and one of the country ’ s leading election experts , said the SNP appeared on the brink of winning 45 of Scotland ’ s 59 seats . Ms Sturgeon , appearing on ITV 's Lorraine show , claimed that if Labour ruled out a deal with the SNP they would be saying they were happy to see David Cameron 'waltz back in to Number 10 ' ‘ That means the formation of any government after May 7 will be with the acquiescence of the SNP , ’ the professor added . ‘ Mr Miliband ’ s chances may indeed depend on him coming to some arrangement with the SNP. ’ Electoral deals between two or more parties can take various guises . A full-scale coalition is a power-sharing deal of the kind struck by David Cameron and Nick Clegg , with a shared programme and ministers from different parties . One step down from a coalition is an arrangement called ‘ confidence and supply ’ . In exchange for concessions to its interests , a smaller party agrees to back a larger one in key Commons votes . A still looser arrangement is possible , whereby a minority Labour government would negotiate with the SNP to win its backing on every major vote . William Hague , the Leader of the Commons , said an issue-by-issue deal between Labour and the SNP would be ‘ even worse ’ . ‘ Every day the SNP could come back with more demands , ’ said the Tory MP . Miss Sturgeon , speaking at the London School of Economics , set out a shopping list of demands for a deal with Labour , including £180billion of extra borrowing , ditching the Trident nuclear deterrent , and billions more in benefits for the working poor . She said the SNP would ensure that any government it supports offered an ‘ alternative to austerity ’ . In the past , the SNP imposed a ‘ self-denying ordinance ’ on its MPs which prevented them from voting on most ‘ English-only ’ issues at Westminster . But , with the possibility of a power-sharing deal in sight , this principle has been ditched . Miss Sturgeon yesterday said SNP MPs were entitled to dictate policy at Westminster in return for their votes . ‘ We have clear and constructive views on many aspects of UK policy which affect Scotland deeply – views which we know are often shared by many people elsewhere in the UK . And we intend to bring those ideas forward in a positive spirit , ’ she said . She insisted that voters in England could trust her not to use a hung parliament as part of a plan to make another attempt to break up the country . Last night an ICM poll for the Guardian revealed 43 per cent of voters are worried about the SNP determining who runs the UK . Labour leader in Scotland Jim Murphy ( left ) said the party would not make any 'backroom deals ' with the SNP .
Plaid Cymru chief said she would vote Green in England and SNP in Wales . But she called for deal with Labour after the election to keep the Tories out . Ms Sturgeon she she would impose left-wing policies across the UK . She said the Plaid Cymru wanted to do more than just serve Scotland 's interests .