Chris Huhne launched an extraordinary attack on frontrunner Nick Clegg in a rowdy exchange on BBC1's The Politics Show.

The row came after Mr Huhne was confronted with a dossier apparently compiled by his campaign team entitled "Calamity Clegg" and detailing alleged policy shifts by his rival.

While insisting he had never seen the document before, Mr Huhne went on to accuse Mr Clegg of "flip-flopping" in areas like Trident and school vouchers.

The environment spokesman said: "I don't support describing anybody else in the party a 'calamity', that's absolute nonsense, but I do think we've had a series of flip-flops on this issue from Nick."

Mr Clegg, Lib Dem home affairs spokesman, said he had repeated his positions until he was "blue in the face", adding that he was "saddened" by the approach taken by Mr Huhne.

Turning to his opponent, he said: "With respect Chris, this contest is not about me meeting false challenges that you put up to me. It's about me saying what I think the Liberal Democrats need to do to the country, for the country, to make Britain a more liberal place."

He added: "I think there is a danger in an internal contest, particularly in these latter stages when people get terribly excited, of saying things to each other which, let's remember, our opponents will use against whichever of us becomes leader. So I refrain from that."

Meanwhile, Mr Clegg's apparent lead in the race to succeed Sir Menzies Campbell was further bolstered as two more MPs - Jo Swinson and Alan Beith - backed his bid for the leadership.

Their announcement took Mr Clegg's support in the Commons to 36, beside himself, well over half the 63 Lib Dem MPs.