Nick Clegg has come under yet more pressure after a fresh assault on his leadership from within the Liberal Democrats.
Senior party figures have warned that the Deputy Prime Minister is not "indispensable" and could be replaced by Business Secretary Vince Cable.
Adrian Sanders, a veteran Lib Dem MP, told The Sunday Times that Mr Clegg had to stop "just bumbling along worrying about the future" and to take action to rebuild support in the party.
His comments were echoed by the Lib Dem peer, Lord Smith of Clifton, a former professor of politics, who told the paper that Clegg was "just a cork bobbing on the waves" with "no strategic vision at all".
"It's not as if Clegg is indispensable. Vince Cable possesses the appeal and the credibility to lead the Liberal Democrats into the next election," he was quoted as saying.
Andrew Bridgwater, vice-chairman of Devon and Cornwall regional party and chairman of the Lib Dem education association, went even further, calling on Clegg to go.
"The sooner Nick resigns and creates a vacancy for Vince, the better," he told The Independent on Sunday. "To put it bluntly, I would encourage Vince Cable to stand for the leadership to take us into the next election."
Their comment came after one of Cable's closest allies, Lord Oakeshott of Seagrove Bay, warned last week that the party may have to consider a change of "management and strategy" if it was to stand any chance at the next general election.
Sir Menzies Campbell endorsed his successor's continued leadership of the Liberal Democrat party.
He told the Sky News Murnaghan programme: "(Nick Clegg) is in charge of his brief and he in charge of his party.
"Of course it is September and it wouldn't be September if there wasn't speculation about the leadership - David Cameron is accused of being a mouse, there are reports Ed Balls is, shall we say, less than polite to Ed Miliband, his leader.
"It's the sort of thing you get in the run up to the party political conferences.
"Perhaps Lord Oakeshott, and others, should get out of the cloistered comfort of the House of Lords and perhaps the seduction of the studio. What Liberal Democrats are doing in Government is an essential part of the strategy.... of course there will be differences of opinion.
"People say sometimes political parties are like coalitions - well the truth is coalitions are like political parties, because you have differing opinions at different times."