Students campaigning against any attempts to introduce "top-up fees" lobbied Parliament on Tuesday.

Hundreds of students visited Parliament in an attempt to build up support among MPs.

They also handed in petitions organised by the National Union of Students (NUS), and signed by 15,000 people, to Downing Street.

The NUS 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 they say they need for research projects and to retain senior academics.

Tuition fees 'set precedent'

Opponents of such a scheme say 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.

The government has consistently opposed the use of top-up fees, with the Education Secretary, David Blunkett, recently reiterating his own opposition.

But the NUS is concerned there is a long-term drift towards placing entry charges on students - following the precedent set by tuition fees.

It is urging MPs to sign an early-day motion in the House of Commons, declaring opposition to top-up fees.

The motion has been signed already by more than 50 MPs.