Politicians who begged Scotland to stay in the Union should not complain if the SNP calls the shots at Westminster after the election , Nicola Sturgeon said last night . Polling last night showed that the nationalists are extending their lead – threatening to all but wipe out Labour north of the border . But Ed Miliband yesterday refused four times to rule out going into a power-sharing agreement with the SNP if its MPs hold the balance of power for the first time . Scroll down for video . Boy , are we doing well : SNP leader Nicola Sturgeon campaigning in Irvine , Ayshire yesterday . During a visit to Lincoln , the Labour leader was asked repeatedly whether he was prepared to dismiss the idea of any pact . While he has rejected a formal coalition he did not address questions as to whether he was prepared to go into Downing Street propped up by Miss Sturgeon on a ‘ vote-by-vote basis ’ . The SNP leader used a BBC TV debate on Thursday night to offer to ‘ lock David Cameron out of Downing Street ’ – even if Labour has fewer seats than the Tories in a hung parliament . She dominated the so-called ‘ challengers ’ debate ’ , and was deemed the best performer by 35 per cent of viewers to the Labour leader ’ s 29 per cent . Yesterday she said : ‘ During the referendum campaign last year , we were told repeatedly by politicians who were trying to persuade Scotland to vote no – and they succeeded – that Scotland was an integral part of the UK , that our view mattered , ’ Miss Sturgeon said . Sturgeon dominated the so-called ‘ challengers ’ debate ’ on Thursday and her party is threatening to all but wipe out Labour north of the border . ‘ It ’ s completely unacceptable now for those politicians to say , when Scotland is perhaps going to make its view heard by voting SNP , to say your voice can ’ t be heard in the UK. ’ She said her MPs – who could number as many as 50 after May 7 – would vote to roll back reform of the NHS in England . Traditionally , Scottish nationalists have not voted on health and matters that do not affect their constituents , since they are controlled in Scotland by the Holyrood parliament . ‘ Ed Miliband knows as well as I know that if there is an anti-Tory majority after the election , then the only way David Cameron gets back into Downing Street is if Ed Miliband is prepared to stand back and let him back in Downing Street , ’ Miss Sturgeon told Sky News . ‘ If Ed does that , then Labour voters in Scotland will never ever forgive him and I suspect Labour voters across the UK will never forgive him . Is he really saying that he ’ d rather watch David Cameron back into Number 10 than work with the SNP to keep him out of Number 10 ? That ’ s for him to answer . ‘ I ’ m fighting for more progressive politics across the UK and I ’ m fighting to get rid of the Tories but crucially to see the Tories replaced with something better , something bolder something that ’ s going to deliver progressive policies for ordinary people not just in Scotland but all of the UK . ‘ Our MPs will vote for a bill to restore England ’ s NHS to its founding principles , ensuring it remains the accountable public service it was always meant to be – and protecting Scotland ’ s health budget in the process. ’ SNP activists insist Scotland has long had to put up with Tory governments , even though the party currently has only one MP north of the border . David Cameron warned last night that voters across the UK would face higher taxes to fund profligate public spending if Labour does a deal with the SNP . The Prime Minister said Mr Miliband must ‘ level with the British people ’ and admit that his ‘ only route into Number 10 ’ is with the support of the SNP . Speaking on a campaign visit to the West Midlands , Mr Cameron said : ‘ The fact is that Labour can not win a majority on their own . They can only get into Downing Street with the support of the SNP . ‘ What is it that the SNP want ? They want more borrowing , they want more taxes , they want more unlimited borrowing – they want all the things that got us into this mess in the first place. ’ Miss Sturgeon ’ s predecessor as Scottish first minister , Alex Salmond , who is bidding to return to the Commons , suggested that an SNP deal with a minority Labour government was ‘ probable ’ . He told ITV News a vote-by-vote arrangement with Mr Miliband would be much more likely than any other agreement . ‘ What I ’ ve said and what Nicola has said , more importantly , confidence and supply is possible , but vote by vote is probable . ‘ The fact that on a case-by-case basis we ’ d be able to vote for progressive ideas , progressive politics , I think is a very powerful position . ’
Polling last night showed that the nationalists are extending their lead . SNP are threatening to all but wipe out Labour north of the border . Comment: Sturgeon used TV debate to offer to ‘ lock Cameron out of Downing Street ’