Ed Miliband has ruled out agreeing to a so-called “confidence and supply” deal with the SNP as he moved to dismiss Tory warnings that Britain would face a constitutional crisis if the Scottish nationalists held the balance of power in a hung parliament.

The intervention by Miliband came as the Conservatives ramped up their rhetoric on the dangers of a post-election deal between Labour and the SNP. Theresa May, the home secretary, said Britain could face its gravest constitutional crisis since the abdication of Edward VIII in 1936. Boris Johnson, the mayor of London, warned of the “deeply alarming” prospect of the SNP “monkey” crawling on Labour’s back.

Ed Miliband v Boris Johnson: pair trade blows over non-dom status - video Guardian

The Labour leader dismissed the Tory claims when he asserted he was not interested in agreeing to deals with the SNP. He told the Andrew Marr Show on BBC1: “I want to be clear about this. No coalitions, no tie-ins … I’ve said no deals. I am not doing deals with the Scottish National party.

“I’m not interested in deals, no … The way the House of Commons works is that we want to put our Queen’s speech before the House of Commons and the other parties will vote.

“I disagree with them on independence. It would be a disaster for our country. There are other big disagreements: on national defence, on the deficit and a bigger philosophy question. The Tories and the SNP now have something in common. They want to set one part of the country against another.”

The Tories have made their warnings about a post-election deal between Labour and the SNP one of their main campaign messages as they seek to win back former supporters who are thinking of voting Ukip. Miliband has ruled out forming a coalition with the SNP and has dismissed the idea of agreeing less formal deals.

In some of his clearest remarks on the issue, Miliband specifically rejected a “confidence and supply” deal in which the SNP would support him on any confidence votes and in budget (supply) votes. Asked by Marr whether he would agree to such an arrangement, Miliband said: “No.”

Miliband spoke out as a YouGov/Sunday Times poll suggested the SNP could win 46 of Scotland’s 59 seats at Westminster. This would give the SNP a pivotal role in a hung parliament. The other seat projections for the main parties are the Tories on 278, Labour on 271 and the Liberal Democrats on 30. This would put the nationalists in a pivotal role because the combined Labour-SNP share of seats would be 317 – nine short of an overall majority. The combined number of Tory-Lib Dem seats would be 308.

The Labour leader appeared on the Marr show after Johnson had warned of the dangers of an SNP-Labour deal. The London mayor said: “There is no way Miliband could conceivably govern except with the help of the SNP. They’d be crouching on his back like a monkey. I think it is deeply alarming … With the SNP pushing him even further to the left there would be a real, real economic risk to this country.”

In the strongest warning issued by a Tory, May said Britain would face its gravest crisis since the abdication of Edward VIII in 1936. The home secretary told the Mail on Sunday: “If we saw a Labour government propped up by SNP it could be the biggest constitutional crisis since the abdication.”

May questioned the legitimacy of SNP MPs at Westminster as she warned of an English backlash if they were able to decide on health and education in England while MPs south of the border had no say on such matters in Scotland. She told the Mail on Sunday: “It would mean Scottish MPs who have no responsibility for issues like health, education and policing in their own constituencies [as they are devolved to the Scottish parliament] making decisions on those issues for England and Wales.

“Rightly, people in England would say: ‘Hang on a minute, why are Scottish nationalist MPs allowed to do that?’ Miliband would be in government on the coat-tails of Sturgeon and Alex Salmond. They would be calling the tune – people who don’t want the UK to exist and want to destroy our country.

“There would be a very real feeling this was something people did not want to see, had not voted for and would find very difficult to accept. It would raise difficult questions about legitimacy. A lot of English people would question that.”

Asked to respond to Miliband’s comments, the deputy prime minister, Nick Clegg, said: “The problem is I don’t know what he’s going to say tomorrow.”

“This is the dilemma for both David Cameron and Ed Miliband,” said the Liberal Democrat leader. “They’re thrashing around making up things on the hoof because they daren’t admit what everybody knows, which is that they’re not going to win an outright majority.

“Which is why you have Ed Miliband changing his tune and he might change his tune again tomorrow.”

Clegg said the country was faced with the “stark choice” of “a minority administration led by Ed Miliband or David Cameron basically at the beck and call of either the right or the left or, the greater likelihood, of a government anchored in the centre ground acting fairly for the whole nation.”





