The joint issues of top-up fees and student finance have dominated a rowdy session of prime minister's questions.

In the half hour session, Tony Blair repeatedly refused to rule out the introduction of top-up fees for British university students.

But he signalled that neither students nor their parents will be forced to pay thousands "up front" for higher education.

Challenged by Iain Duncan Smith to say whether he backed Gordon Brown's view that the fees were a "ridiculous idea", the prime minister insisted that the status quo was not an option.

"We have to change the existing system," he said.

The Labour leader, who is said to back a system of top-up fees, said that money could only "come from three sources - the taxpayer, the student or the parents".

"The one thing that is absolutely clear is that the status quo is not an option because universities need more money," said Blair.

"They need more money because we have a situation...in which funding for higher education was cut per student by 36 per cent under the last government.

"Student staff ratios have doubled, there is an £8 billion backlog of repairs and investment required and therefore we have to change the existing system."

But the Tory leader said the prime minister and Gordon Brown were increasingly at loggerheads over the issue.

Quoting the chancellor's words at a recent breakfast meeting with journalists, Duncan Smith said: "What is the point of a review if the chancellor has already made up his mind."

"The chancellor is going around saying completely different things than the prime minister."

"When the chancellor said he was in favour of graduate taxes was he right or was he wrong?"

Insisting that "everybody agrees we need more money for universities", Blair warned it would be absurd to pre-empt the government's review of higher education funding.

The prime minister said the government would strive to increase access to students from all backgrounds.

"There will be a review, we will publish it in January. And let me tell him what it will do," said Blair.

"It will increase access to university. It won't mean that parents will are having to pay up front thousands of fees and it will allow people the chance to go the university which this side favour and he doesn't."

Lib Dem leader Charles Kennedy also sought to expose a growing rift at the heart of government.

"Given that the prime minister has again confirmed that the status quo is not an option where university education funding is concerned, could he therefore confirm is he in fact saying to us this afternoon that top-up fees remain under active consideration by the government," said Kennedy.