Charles Kennedy has challenged Tony Blair on his plans for university top-up fees.

The Liberal Democrat leader, who this week outlined his opposition to the introduction of variable student fees, reminded the prime minister that in 2001 he had said Labour would not introduce top-up fees.

Answering question in the Commons, Blair claimed that the pledge had been for the length of the current parliament.

"We have made it clear that because of that commitment we cannot introduce the in this parliament," he said.

Kennedy criticised the response as a "lawyer's answer".

"Given what he said before and proposes to do now how can the British people trust him or his government?" he asked.

Blair said the next general election would provide a mandate for the scheme.

"The issue at the next election will simply be this: how do we fund universities better, how do we improve access for our students," the prime minister claimed.

"[The Conservatives] want to cut the number of students and cut the funding.

"The policy of the Liberal Democrats is to say that they agree universities need, more money, they agree with widening access and this is to come out of a 50p top rate of tax.

"Except the problem with that policy is that it is not merely the top rate of tax that is going to pay for student fees, it is going to pay for their plans for care for the elderly and also for increases in the National Health Service."