Alan Johnson says for every �1 a student pays, �14 comes from the taxpayer

While defending the central principles of the government's plans for university funding, Mr Johnson said that "refinements" were possible.

Speaking in a BBC News interactive forum, Mr Johnson reiterated that the overall deal for students was fair.

And he argued that there was a strong economic case for increasing the number of university places.

Rebellion

The fees plans, which will allow universities to charge up to �3,000 per year, have provoked threats of a rebellion by Labour backbenchers - who argue that poorer students will be deterred from entering higher education.

It's going through the parliamentary process, there's always the opportunity for refinement Alan Johnson, Higher Education Minister

While re-stating that the government would not give ground on the general principle of variable, student fees - the minister suggested that there was still scope for debate over benefits for poorer students.

"It's going through the parliamentary process, there's always the opportunity for refinement," said Mr Johnson.

"The central planks of this policy remain - end of up-front fees, fee deferral, no real rate of interest applied, the ability of universities to decide what to charge for an income stream that they have total control over, between �0 and �3,000. We will not change our minds on these issues."

But he suggested that the details of support for poorer students could still be open to discussion.

"We are willing to look at the package - we've already outlined the �2,700 paid up front, rather than a combination of grant and fee deferral - and we will look at that very closely and will have a full discussion about that."

"But on the general theme, we have made up our minds," said the higher education minister.

'Free at point of use'

Defending the tuition fees plan, Mr Johnson said that it represented a good deal for students - saying that it meant that for every �1 paid by a student, the taxpayer would be contributing �14 towards their university costs.

As repayments would only be made once students had begun working, he said that it was an improved system - with university becoming "free at the point of use".

Challenged on whether the fees policy was a U-turn - after Labour's manifesto commitment not to introduce top-up fees - Mr Johnson said that top-up fees were fundamentally different from the variable fees now being proposed by the government, as they set an upper limit.

But Mr Johnson conceded that a "fair point" was being made by critics who had e-mailed to say the proposed system could unfairly advantage students from poorer families who end up in high paying jobs.

These students, who even if they become high earners, could be re-paying less than fellow former students from better-off families.

The minister emphasised the importance of looking at the wider economic picture of increasing the number of graduates - saying that in a "knowledge driven economy" the country would depend on a well-educated population.

The expanding employment areas were for graduates, he said, and that it was out-of-date to suggest that increasing university numbers would mean a reduction in quality.