A leading Liberal Democrat has challenged potential rebels in the party to justify themselves, in a sign of deepening divisions over tuition fees in the party.
Lib Dem parliamentary party chair Lorely Burt has challenged MPs opposed to the party's tuition fees U-turn to justify their position in an interview with politics.co.uk.
In a further sign that abstentions within the coalition agreement are now nearly irrelevance, she admitted it would be "incongruous" for Lib Dem Vince Cable to vote against his own tuition fee proposals.
The business secretary has staunchly defended the coalition government's plans to nearly triple the maximum cap on tuition fees to £9,000, despite signing a pre-election pledge to oppose any rise.
Many backbenchers are understandably reluctant to go back on their pledge, but Ms Burt backed attempts by deputy prime minister Nick Clegg to bring them into line.
She said the shift was justifiable because Lib Dem policy commitments from the party's manifesto did not reflect the changed realities which emerged after polling day.
"We went into the general election with the full and certain belief that what we had proposed and fully costed was doable," Ms Burt told politics.co.uk.
"What's now clear is that the position was very far from what we had originally thought so we're now in a situation where yes, we can stick to our principles, but where does that leave a first-class world higher education system?
"Those people who say 'I'm being pure and sticking to my principles' - they must say how they would find the money to keep our world-class higher education system."
Tuition fees had been thought of as non-negotiable during the talks which formed the coalition government.
The coalition agreement stated that if the government's response "is one that Liberal Democrats cannot accept... then arrangements will be made to enable Liberal Democrat MPs to abstain in any vote".
Mr Cable's support has technically ruled out the need for an abstention, but discontented Lib Dem MPs are still talking about splitting three ways - between support, abstaining and outright rebellion - when the issue finally comes to a vote.
"I think it would be incongruous for a secretary of state to advocate a specific position and then abstain. So I think Vince will need to vote in favour," Ms Burt added.
"It's the politics of coalition. We understand the reality we have to operate in."