The Tories have launched a new campaign warning of what they call the "nightmare" of a Labour/nationalist coalition at Westminster after May's election.

"The SNP would prop up Ed Miliband - meaning chaos for Britain," says a new poster which is already sparking furore on social media.

The campaign, sparked by a poll suggesting Scottish nationalists could hold the balance of power in the UK, comes after First Minister Nicola Sturgeon refused to rule out an alliance with Labour. She has, however, said she would not work with Conservatives.

The poster features Mr Miliband hugging Alex Salmond - not Ms Sturgeon - outside 10 Downing Street.

Twitter users south of the border - many of whom see Mr Salmond as a bogeyman - immediately responded to the image.

"Vote Labour, Get SNP," joked one. "Well we don't want those two jokers," tweeted another. "And that goes for Scottish Independence though the back door! Not on, Alex!"

Scottish Conservative leader Ruth Davidson tweeted:. "An Ed-Eck deal is scary for all unionists."

A senior Tory source said:: "Ruth has been making the point same point as this poster for weeks now - Nicola Sturgeon and Ed Miliband are halfway down the aisle.

"This poster is aimed at everyone across Britain and it doesn't matter where you live, the same point applies - between them Labour and the SNP would cause chaos."