Tim Farron, the Liberal Democrat president, called for the Coalition's controversial plans to bring in university tuition fees to be torn up.
His comments will dismay Nick Clegg, who has insisted that the party, which suffered huge political damage over the scheme, attempts to "sell" the proposals to the public.
Mr Farron told a Channel 4 fringe meeting that the move to introduce fees of up to £9,000 a year for students, was "still a black cloud" over the party. He said: "If we had the chance, it should certainly go. We should go some way to undoing it and replacing it with something fairer."
Mr Farron, regarded by many as the left-wing conscience of the party, denied he had leadership ambitions and insisted he would never challenge Mr Clegg. He said: "If Nick Clegg wanted to quit, I'd nail his feet to the floor." However, he refused to rule out ever standing for the top job.
Striking a note at odds with the leadership, he said he regarded the privatisation of energy companies by Tory governments in the 1980 and 1990s as a major mistake. "How much easier would it be to achieve a green recovery if we still owned our energy companies," he said.
He argued that Norway's success in extending broadband coverage to 99 per cent of the country was because they "weren't so stupid to sell off their telecoms industry".
Mr Farron also mounted a surprise attack on Asda, the sponsors of the Birmingham conference. "I'm slightly embarrassed that the conference is sponsored by Asda, given what they do to British farmers. It's a good supermarket, a good employer – and they're only doing what they're allowed to. We have an unfair system, that allows them to exploit the little man."
Mr Farron, who has made delegate-pleasing attacks on the party's Tory partners this week, dismissed any suggestions of an election pact with them – or that they would be seen as too close to them at the next election.
"The idea we have made a long- term ideological commitment to the Conservatives is absolute pants. We are two separate parties... but it is polite, it is permanent." Mr Farron also attempted to row back from comments he made earlier this week suggesting that the Coalition could break up in three years' time, insisting he meant three years and eight months, which is when election campaigning will begin.
* "If [the Coalition] is a marriage, it is a good-natured one but I am afraid it's temporary."
* "I don't want to upset you and it is not going to happen for three or four years, but I am afraid divorce is inevitable."
* "The super-rich do not need to go down Ealing High Street nicking TVs to demonstrate contempt for society."
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