Top up fees must be introduced to ensure Britain's elite universities are able to maintain their position among the world's best, Tony Blair has told the BBC.

The prime minister said graduates from institutions like Oxford and Cambridge would be asked to pay more than those going to many other universities.

He said the alternative would be using an even greater slice of ordinary taxpayers' money to support the colleges.

Speaking on BBC 1's Breakfast with Frost programme Mr Blair also said there would be no "positive discrimination" to favour applications from poorer students, as some reports had suggested.

He said the establishment of an access regulator was: "Simply to make sure that universities are doing their best to go out and tell some of the kids from the poorer schools, 'this is something you can do'."

'Conundrum'

Attempting to placate fears about the rising cost of a university education, Mr Blair said top up fees would only be repaid by those earning above a certain level.

Although all students pay the same their is a huge additional amount of public tax payers money that goes to the top universities Tony Blair

He also claimed it was better than the current system because students and their parents would no longer be asked to pay fees in advance.

Mr Blair said the government faces a "conundrum" over university funding and that reform - including tuition fees of up to �3,000 a year - was necessary.

"At the moment - although all universities charge the same fee - the amount of public money that goes, for example, to Oxford, is four times the amount that goes to Wolverhampton University, though they have the same number of students.

"So although all students pay the same their is a huge additional amount of public taxpayers money that goes to the top universities.

"On the other hand, unfortunately, if you compare Cambridge with Harvard in the United States (it) has about half the money."

Mr Blair added: "They need more money, we are giving them more, but if they need even more money it is surely right that they raise some of that by way of repayment from students once they graduate."

Increased debt

The plans are part of a wide-ranging and long-awaited shake-up of higher education in England.

Universities will be able to charge fees up to �3,000 and students will not have to pay until they graduate, and begin to earn at least �15,000.

However, students and academics warn the plans could lead to a "two-tier" system and could saddle students with increased debt.

They fear the re-introduction of maintenance grants for the poorest students, and the creation of an "access regulator" will not be enough.