PLOTTERS against Ed Miliband have been attacked as backers of his brother David who have never accepted the result of the Labour leadership contest.

Reports at the weekend suggested as many as 20 shadow ministers would back a coup if former home secretary Alan Johnston signalled he was willing to take over.

But Lucy Powell, newly appointed vice-chairwoman of the party's General Election campaign, told secret critics to put up or shut up. She said: "Either show us your colours and put names to quotes or let's just move on and have a different conversation."

Glasgow South West MSP Ian Davidson said: "As far as I can see, all of this speculation is simply froth started by people who have never been reconciled to Ed's victory over David, who they still toast as the king over the water."

However, Shadow Energy Secretary Caroline Flint admitted Labour MPs were nervous about Mr Miliband's leadership. She said: "Some of my colleagues are having jitters and part of that is we've always said this is not a done deal, this election, this is going to be hard fought, and we said that from 2010 and Ed has been saying it since he was elected our leader.

"We have to fight for the right to represent the country in Westminster."

Former Labour leader Lord Kinnock admitted the headlines about Mr Miliband were serious, but dismissed the danger to his leadership as unsubstantial because it had come from anonymous sources. He said: "The so-called threat, and I emphasise so-called, is certainly not substantial - not only because all of the sources of the so-called threat are common in their anonymity and cowardice and as far as I can see their tendency towards political suicide.

"But because there is no real substance in what they are saying, the claims they are making in so far as you can ­identify them are totally unjustifiable."

Gordon Brown's former spin doctor Damian McBride accused Mr Miliband of "fluffing" the opportunities he has had to restore his authority within the party.

He said: "If anyone was prepared to come forward now and actually do a formal challenge, I think the Miliband camp would fold very quickly."

Polls showed that even Labour voters were losing faith in Mr Miliband as a credible premier.

Shadow health secretary Andy Burnham and shadow home secretary Yvette Cooper dismissed reports they intended to present a joint platform in the event of a leadership vacancy.