Ed Miliband has accused the SNP of working for a Conservative victory in May's General Election.

The Labour leader levelled the accusation during a campaign event in Clydebank - where he arrived to more bad news from the opinion polls.

According to a new analysis by Scotland's leading polling expert, Professor John Curtice, his party could be left with just two MPs North of Border as the SNP capture 53 out 59 seats.

Mr Miliband used a speech to supporters to highlight differences between Labour, Conservative and SNP economic policies.

In a Q and A session after the speech, he was asked whether Mr Salmond - who talked up SNP hopes of a post-election deal with Labour at the weekend - had Labour "over a barrel".

The Labour leader said: "There seems to now be an unholy alliance between the Conservatives and the SNP to carry on a Tory Government.

"Frankly Alex Salmond is at it again."

He accused the former First Minister of "bluster and bluff," adding: "I gather he's got a book to sell."

Mr Miliband hit out after Mr Salmond said the SNP would support a minority Labour government on a vote by vote basis.

The Conservatives seized on his comments, issuing a new campaign advert saying Mr Salmond would "call the tune" if Mr Miliband became Prime Minister.

Mr Miliband went further than he has before in playing down the possibility of an informal power sharing deal with the SNP after the election.

He said: "I'll tell you who is going to be writing a Labour Budget, it's me and Ed Balls. Not Alex Salmond in a million years.

"It will be for other parties to decide how they vote on Labour's Queen's Speech."

In his speech, Mr Miliband said last week's Budget provided a "dramatic illustration" of the differences between Labour and Conservative economic plans.

He said only Labour could end the Tories' ideologically driven austerity programme.

He also hit out at the SNP's demand for devo max, which he claimed would leave Scotland £7.6billion worse off next year.

Shadow Foreign Secretary Douglas Alexander has previously accused the SNP of working for a Conservative victory, arguing the Nationalists would welcome David Cameron's return to Downing Street in the belief it would increase support for independence.

The new Guardian ICM poll put support for the SNP on 43 per cent and Labour on 27 per cent, virtually unchanged since December.

On a uniform swing, the SNP would win 43 seats to Labour's 12.

However, Professor Curtice said Labour could be reduced to two - holding Glasgow North East and winning East Dunbartonshire from the Lib Dems - as former Labour heartlands were turning to the SNP in bigger numbers than elsewhere.