Simon Hughes, the Lib Dems' new deputy leader, has vowed to ensure the party retains a "clear and distinct" voice aside from its role in the coalition.
Elected to the post on Wednesday, the MP said he would have more freedom than leader and Deputy Prime Minister Nick Clegg to speak out on some issues.
He said he hoped the Lib Dems would "win the argument" on tuition fees - where they disagree with the Tories.
The coalition deal permits Lib Dem MPs to abstain on any move to raise fees.
The party has long been opposed to tuition fees and former Lib Dem leader Sir Menzies Campbell said recently that he would vote against any proposal to raise the current cap on what students pay in England and Wales.
Mr Hughes told BBC Radio 4's Today that people should not pre-judge the outcome of a review of fees by the former BP boss Lord Browne or how the coalition partners would react to its findings.
The review's recommendations would have to be judged against what impact they would have on student finances, the quality of teaching and efforts to boost social mobility, he said.
"We have a distinctive policy. We have said we are opposed to tuition fees," he said.
"Only if we don't manage to persuade the government as a whole to come to a sort of response we are all comfortable with do we get into territory where we would go our different ways.
"I am hoping we don't get there... I hope we can win the argument that won't add to tuition fees and debts for students."
Mr Hughes said the coalition's arrangement over tuition fees - including an abstention clause for Lib Dem MPs in the event of a proposal to raise fees - had been carefully crafted and was "good".
Asked if he would abstain in that event, he said: "That's the agreement. That's the deal."
Pressed further whether he would be prepared to vote against, he said: "I am not saying that."
Mr Hughes saw off a challenge from Tim Farron to win the deputy leadership, taking the votes of 38 of the party's 57 MPs. Mr Farron won 18 votes with one MP abstaining.
Neither he nor Mr Farron was given a job in the coalition government and both have suggested the Lib Dems should have "shadow" ministers for Whitehall departments where their parliamentarians are not represented.
Asked about what role he would play as deputy leader, he acknowledged the party was in "new territory".
"There is a particular benefit, I hope, in having a leader who is in government and a deputy leader who is not a minister that the whole of the Lib Dem party and our message and our voice, can be heard clearly and distinctly from the fact we are also in coalition.
"By definition, being in coalition does not mean we cease to be Liberal Democrats with the views and ideals and characteristics that come with that party, with that great tradition.
"There will an ability to say things about the position of the Lib Dem tradition that, by definition, Nick Clegg cannot do in the same way because he is in a coalition government of which, of course, we are supporters and part."
An MP since 1983, Mr Hughes has served as the Lib Dems' president and was energy and climate change spokesman before the election.
He replaces Vince Cable, who stood down from the deputy leadership role last month to concentrate on the job of business secretary.