The Conservatives are facing a backlash after releasing another general election poster warning voters of what they call the 'nightmare' of a Labour/SNP coalition.

The new poster features an image of Ed Miliband in Alex Salmond's coat pocket.

David Cameron tweeted the image, with the message "Alex Salmond with Ed Miliband in his pocket. The frightening prospect we must avoid" today.

The poster has been criticised by Twitter users, who described it as "infantile and pathetic".

David Henry tweeted: "The #Conservatives have nothing positive to offer so try to demonise Alex Salmond. He was only MP to stand up against Poll Tax."

Andy Briss said: "Infantile and pathetic at the same time-But since #Cameron refuses to debate anything we won't know if he approves of it."

Jonny Gellar tweeted: "Irony of this Conservative poster is that it makes Salmond look more presidential than Cam?"

Kendrick Lamar said: "@David_Cameron how about you just focus on running the country and avoid showing off your Photoshop skills."

Mark Russell tweeted: "@David_Cameron so this is the positive campaigning you said you wanted?"

L Janta-Lipinski said: "Only problem with that Tory poster, given polls and electoral arithmetic, could just as easily stick Cameron in Salmond's pocket."

In January the Conservatives released their first poster warning of what they call the "nightmare" of a Labour/nationalist coalition at Westminster after May's election.

The poster featured a picture of Ed Miliband with his arm around Alex Salmond outside 10 Downing Street and the slogan "Your worst nightmare... just got worse".

Shadow chancellor Ed Balls said today that a coalition with the SNP after the May 7 general election is "not part of Labour's plans".

Mr Balls and other senior figures within the party have come under increasing pressure to end speculation a pact may be on the cards, after polling suggesting the Scottish National Party is set to seize large numbers of seats from Labour north of the border.

Prime Minister David Cameron has said Ed Miliband should explicitly rule out a deal with the SNP "if he cares about this country".

Asked if he could categorically rule out a deal with the nationalists, Mr Balls said: "The SNP have said they don't want a coalition. It's not part of our plans. We don't want one, we don't need one, we're not after one.

"No large party in the last 100 years - Labour or Conservative - has ever fought a general election on the basis they wanted a coalition or deal with a small party.

"It's the last thing we want. What we want is a majority Labour government."

Mr Balls suggested that Conservatives were raising the prospect of a Labour-SNP deal to divert attention from Mr Cameron's refusal to take part in three leaders' debates planned by broadcasters during the election campaign, and from Tory plans for cuts in public spending, which he said could total £70 billion over the course of the next parliament.

Mr Balls said: "We have had for the last 48 hours a scare from the Conservatives about SNP coalitions. Why do you think they are doing that? Because David Cameron doesn't want to debate why he won't do the debates and he doesn't want to debate where he is going to get £70 billion of spending cuts.

"It is a complete nonsense argument. We want a majority and that's what we are fighting for."

The SNP's leader in Westminster, Angus Robertson, said: "On issue after issue, Labour find themselves on the same side of the argument as the Tories - which is the wrong side for the people of Scotland.

"The polls continue to show Labour are deeply unpopular in Scotland. The reasons for this are Labour's toxic alliance with the Tories in the referendum and convergence on Tory ground by voting with them for £30 billion more austerity cuts.

"People want Scotland to have a powerful voice at Westminster, and only a strong team of SNP MPs elected in May can achieve the change that people in Scotland want - including the alternative to austerity. Only SNP MPs can achieve change - power for Scotland, and the delivery of progressive policies across the UK."

Liberal Democrat leader Nick Clegg told a policy launch in east London: "Our view is that, in the same way we would not countenance putting Ukip in charge of the EU, we would not countenance putting the SNP in charge of a country that they want to rip apart.

"It's as simple as that."