The defection of an independence campaigner to Labour amid claims SNP figures privately want another Tory government has been dismissed by the nationalists as a case of "sour grapes".

Muhammad Shoaib, who led the Scots Asians for Independence movement during the referendum campaign, has resigned from the party claiming SNP colleagues were "secretly hoping" for the Tories to form the next government in order to hasten another vote on the issue.

The former Pollokshields SNP branch convener said he will now throw his weight behind Labour in an effort to ensure Ed Miliband is prime minister.

It follows claims in a leaked Whitehall memo that Nicola Sturgeon would rather David Cameron was prime minister, allegations which the SNP leader has vehemently denied.

Businessman Mr Shoaib, 62, told the Daily Record newspaper: "I have been a senior member of Nicola Sturgeon's constituency for years and I am deeply saddened that many of my former colleagues in the SNP secretly hope for another Tory government.

"I have become more and more shocked that many in the SNP want to put the interests of the SNP before the interests of Scotland, and their secret hopes for a Tory government betray their true motives. I can no longer stay silent and stand idly by.

"That is why today I am backing Labour as the only party big enough and strong enough to kick the Tories out."

Former Scottish Labour deputy leader Anas Sarwar said on his Facebook page: "Delighted to get the endorsement and support of leading SNP member and organiser of Scots Asians for Independence Mohammed Shoaib."

Responding to the defection, the SNP said Mr Shoaib had been unsuccessful in an attempt to be selected as the party's candidate in Glasgow Central.

A party spokeswoman said: "The SNP have gained 3,000 new members in the last few days.

"Given that former Labour councillor Muhammad Shoaib tried and failed to be selected as an SNP parliamentary candidate just a couple of months ago, this is a clear case of sour grapes.

"People in Scotland know that the way to keep the Tories out and give Scotland a strong voice at Westminster is to vote SNP."

The SNP also drew attention to comments made by Mr Shoaib in December in which he said the Labour Party had "shifted toward right-wing politics" and that the party's social justice ethos "has gone out of the window".

Mr Shoaib is also quoted attacking Scottish Labour leader Jim Murphy for "basically supporting an illegal war in Iraq".