ED Miliband and Jim Murphy yesterday failed to rule out a power-sharing deal with the SNP after the general election, despite increasingly frantic demands from the Conservatives to do so.

In a clear sign Labour now views the SNP as a potential Westminster partner, given the latter's poll ratings, the UK and Scottish leaders defied repeated calls to rule out a Lab-Nat pact.

In their speeches at the Scottish Labour conference in Edinburgh, both men also conspicuously refrained from attacking the SNP, despite the party being their main electoral opponent in Scotland, another clue that Labour is keeping the door open to a future alliance.

Press reports overnight claimed Miliband would use the occasion to rule out a deal.

Murphy did, however, rule out a coalition with the Tories as a "no brainer", but repeatedly ducked questions on a deal with the SNP to put Miliband into Downing Street.

He said: "I'm not going to go into a post-match analysis of an event that has not taken place.

"If the SNP want to vote for our policies that's up to them. To get involved in all of this before people have had a chance to vote, I think it's pretty disrespectful."

Labour's thinking emerged after a series of senior Tories urged Miliband to reject an arrangement with the SNP for the sake of the UK.

Last week, the former Conservative PM Sir John Major warned the SNP would enter any deal with Labour with the overriding aim of "prising apart" the Union.

Overnight, former Tory party chair Lord Baker even called for a "grand coalition" between Labour and the Conservatives to deny the SNP more power.

The former education secretary said a Lab-Nat pact would be a "nightmare" and "stretch the constitution of our country to breaking point".

He said a deal was unthinkable at present, but pointed out that in Germany Angela Merkel's Christian Democrats govern with the Social Democrats.

"What is at risk is the continuing unity of the United Kingdom," he said. "In order to preserve that unity another way should be found.

"This could be a joint government of the Labour and Conservative parties."

Murphy later ruled out the grand coalition plan as "ludicrous".

Speaking in Harrow yesterday, Cameron called a Lab-Nat pact the "worst outcome" in May.

He said: "You could end up with an alliance between the people who want to bankrupt Britain and the people who want to break up Britain.

"Even today, Ed Miliband will not rule out a deal or backing from the SNP.

"If he cares about this country, he should do so. You cannot let the people who want to break up our country into the government of our country."

In his conference speech to delegates, Miliband virtually ignored the SNP in order to present the election as a straight choice between Labour and the Conservatives, and said Scotland would decide Cameron's fate.

Warning people against voting SNP in the hope of ousting the Tories, he said: "Every vote cast for another party, including the SNP, makes the prospect of a Tory government more likely.

"It is just a matter of arithmetic. Because every one less Labour MP makes it more likely the Tories will be the largest party.

"It is the people of Scotland who can help decide this election.

"It is the people of Scotland who can help boot out this Tory government.

"I'm asking people in Scotland to vote Labour to get rid of the Tories and their failed austerity plan.

"I am asking people here in Scotland to vote Labour for a society and economy founded on different values, not simply a government run on the basis of different management."

Miliband also accused Cameron of "duplicity" and being "chicken" over his refusal to engage in all the TV election debates.

He said the Prime Minister's action had exposed a fatal lack of leadership.

After quoting Cameron's past enthusiasm for TV debates, he said: "It is on the issue of leadership debates that David Cameron's duplicity has caught up with him.

"He says this election is all about leadership, all about the choice between him and me, and when it comes to a debate between him and me, he's running scared.

"I say to David Cameron: "You can try to chicken out the debates, but don't ever again claim that you provide strong leadership'."

Scottish Tory leader Ruth Davidson criticised both Murphy and Miliband for failing to rule out the prospect of a post-election deal with the SNP.

She said: "This has been Scottish Labour's 'don't-mention-the-deal' conference.

"Ed Miliband and Jim Murphy spoke about everything except the one thing that Scots want to know - what concessions will they hand up to the Nationalists as part of the deal the two parties are cooking up?

"To simply ignore this key question as they have done at this conference betrays Labour's arrogance and also their weakness."

SNP depute leader Stewart Hosie said: "This speech confirms the utter hypocrisy of Ed Miliband's party, and confirms why Labour's vote is melting away in Scotland.

"His claim that the next UK Government will be determined by who gets the most seats is Labour's big lie in this campaign.

"He is plain wrong - it will be determined by who can command a majority in the House of Commons.

"If there are more anti-Tory MPs in the House of Commons than Tory MPs, the only circumstances in which David Cameron could walk back into Downing Street is if Labour let him - the SNP never will.

"It is time Labour faced reality - they are not going to win a majority in the House of Commons, and will need the votes of others to govern."