Deputy Prime Minister Nick Clegg has insisted he would "never, never, never" join the Conservatives, saying: "I will be carried out in my coffin as a card-carrying Liberal Democrat".
Mr Clegg's forthright denial that he is tempted by a move to David Cameron's party came as Labour leader Ed Miliband made moves to woo left-leaning Lib Dems to defect, while Conservative backbenchers suggested that those on the right of the party should consider taking the Tory whip.
The Liberal Democrat leader was coming under massive pressure to reassert his party's identity within the coalition Government after his humiliating defeat on electoral reform and in elections to English councils, the Scottish Parliament and the Welsh Assembly.
But he insisted that the Lib Dems had "a platform from which we can recover" after scooping one vote in seven in Thursday's elections.
Asked on BBC1's Andrew Marr Show whether he could ever envisage joining the Conservatives - and perhaps taking a Tory peerage - Mr Clegg replied in shocked tones: "Join the Conservatives? No, never. I am not a Conservative - never have been, never will be. Never, never, never.
"I am a Liberal Democrat to my core. I will be carried out in my coffin as a card-carrying Liberal Democrat."
Meanwhile, Ed Miliband appealed to Liberal Democrat ministers to pull out of the coalition, saying local election results showed voters resented the Lib Dems propping up the Conservatives.
He told the show: "Liberal Democrat ministers must hear that they had a real message from the electorate from their former voters. The message was 'we didn't vote for many of the things you're doing. You are being led by the nose by a Conservative Government. Change course on tuition fees, on economic policy.'"
And he addressed Lib Dem Cabinet ministers such as Vince Cable and Chris Huhne directly, saying: "You should change course, you should have the courage of convictions you went before the electorate with a year ago. Frankly, if I was in your position and didn't get that change in direction, then I wouldn't stay in this Government."
Mr Miliband claimed voters saw Labour was a suitable opposition, and pointed to gains in Thanet and Thurrock, and winning control of Gravesham, as evidence of a resurgence in southern England. "We have got to be a truly national party fighting in the south as well as the north. We made progress," he said.