The Lib Dems apologised on Wednesday for promising to scrap university fees before the 2010 election - a pledge they broke once in power by agreeing to a hike in tuition costs.
The centre-left Lib Dems' popularity plummeted after the 2010 election and a series of reversals on key areas of party policy - such as education and austerity - following their decision to join forces with the centre-right Conservatives.
Political analysts say an apology for the U-turn on university fees is necessary for the party to begin to win back the trust of both core supporters and floating voters before the next election in 2015.
The coalition's move to raise the maximum annual limit on tuition fees nearly three-fold to 9,000 pounds in England and Wales triggered angry protests in 2010.
"I shouldn't have committed to a policy that was so expensive when there was no money around. Not least when the most likely way we'd end up in government was in coalition with Labour or the Conservatives, who were both committed to put fees up," Lib Dem leader Nick Clegg said.
"There's no easy way to say this: we made a pledge, we didn't stick to it - and for that I am sorry."
The Lib Dems, preparing for their annual conference next week, are seeking to rebuild support ahead of the 2015 election, Opinion polls put them on about 10 percent, far below the 23 percent they scored in 2010.
"I suspect people have already made up their minds on this, but it's an attempt to draw a line in the sand," said Manchester University politics professor Andrew Russell. "But it does look like the last card in a particularly weak hand."
"It is an attempt to defuse some of his opponents' most potent weapons. The Lib Dems desperately want to talk about other matters."
Clegg decided to make the unusual apology after a series of question-and-answer sessions with voters where the issue was consistently raised.
(Additional reporting by Tim Castle; Editing by Kevin Liffey)