Student leaders are calling on universities to commit themselves to rejecting any attempts to introduce 'top-up fees'.

The National Union of Students is worried that leading universities are planning to increase their budgets by levying a fee from students - in addition to tuition fees and living costs covered by student loans.

The top-up fee system would allow universities to set their own charges, allowing them to raise the extra funds that universities say they need for research projects and to retain senior academics.

Opponents of such a scheme say that this would put the most prestigious universities beyond the financial reach of many students and would create a two-tier system based on wealth rather than ability.

'Equality, not elitism'

The government has consistently opposed the use of top-up fees, with the Education Secretary David Blunkett re-iterating his own opposition last week.

But the NUS is concerned there is a long-term drift towards placing entry charges on students - following the precedent set by tuition fees - and has supported an early-day motion in the House of Commons declaring opposition to top-up fees, signed by 38 MPs.

The union is calling on universities to commit themselves to a system based on "equality, not elitism". The arrival of top-up fees would end the principle of equal access to higher education, says the union.

"Top-up fees would take higher education back into the dark ages of elitism and social privilege. They would be a barrier to access and would create a system which discriminated against students from less well off backgrounds," said the union's president, Andrew Pakes.

Representatives of a group of leading universities - known as the Russell Group after the London hotel in which they have met - discussed top-up fees on Friday, at the University of Warwick.

Following the meeting, the group said it had agreed to commission a team of economists to undertake a full appraisal of different funding options and the practical implications of their implementation.

A statement released by the University of Warwick said: "The vice-chancellors confirmed that the only system acceptable to them would guarantee access to higher education for all students that could benefit from the opportunity, regardless of personal circumstances."