The SNP have hit out at Labour's plans to offer the nationalists nothing in return for propping up an Ed Miliband government at Westminster.

A source said that Labour was in denial and refusing to "face the reality" of minority rule.

The Herald revealed yesterday that Labour MPs have been briefed that Mr Miliband plans to offer the SNP no policy concessions if Labour is the biggest party after May but without a majority at Westminster.

Instead, Labour will ask Nicola Sturgeon's party to support its policies because they would help Scots.

The party would also accuse the SNP of backing the Tories if it voted against a Labour government.

On Tuesday Labour leader Ed Miliband publicly ruled out a formal coalition with the SNP.

However, his statement appeared to leave the door open to a informal deal with the nationalists on a vote-by-vote basis, so-called 'confidence and supply'.

But Labour MPs were told on Tuesday afternoon that that option was also off the table.

A source said that the message had been "unambiguous".

He said: "We can't, of course, physically prevent the SNP voting with us. But we are not going to give them anything for it. What are they going to do? Back the Tories?"

An SNP source said: "Unlike Labour, the SNP know all about running a minority government (at Holyrood) - and the reality is the government has to negotiate with opposition groups all the time, every week of every year, instead of having a single negotiation to agree a coalition.

"That can deliver big dividends for a strong SNP group over a parliamentary term - so our priority is working hard to deliver that big group, and we take nothing for granted.

"Sooner or later, Labour are going to have to face reality - they are not going to win a majority in the House of Commons, and would need the votes of others to govern."

Earlier Scottish Labour's deputy leader Kezia Dugdale refused to be drawn on the issue.

But she said: "The simple choice for the SNP will be do they want to back Labour laws or do they want to vote with the Tories?

"And that is going to apply to every single decision that would come their way if Ed Miliband was Prime Minister.

"If you want a progressive government, if you want taxes like the mansion tax... you have to vote with Labour to get that and that is the vote that Nicola Sturgeon is going to face."

Ms Sturgeon initially reacted to Mr Miliband's announcement, saying: "This was a lot of hype to rule out something no-one was proposing. Miliband's statement is absolutely fine from our point of view."

Later, however, she said that the message that Mr Miliband was sending to Scottish voters was "that he would rather see David Cameron in Downing Street".