More than 25,000 students are expected to demonstrate this afternoon against British government plans to treble them to tuition fees to £3,000 sterling a year.
Crowds have started to gather for the protest march through central London, followed by a rally in Trafalgar Square, organised by the National Union of Students (NUS).
They are expected to be joined by teachers and other workers, who said top-up fees would put working class children off applying to university and damage public services.
Mr Tony Blair and Education Secretary Mr Charles Clarke said this week that they were looking at ways of ensuring the full fee was subsidised for the poorest students once the higher charges - if endorsed by Parliament - come into force in 2006.
Mr Clarke said last Monday that between 35 per cent and 37 per cent may get the full cost covered, although the Prime Minister refused to give a figure.
The subsidies would probably come in the form of remission of the first £1,125 - the current annual charge - plus bursaries from universities themselves, paid or out of their increased fee income.
But their assurances failed to mollify opponents, who say people are already leaving university with debts of £20,000 or more.
Mr Clarke was confronted by an angry mother of a Swansea University student at an event intended to highlight his efforts to attract more state school pupils into higher education.
Jan Krall, a parent-governor at Phoenix High School in White City, west London said her son Steven expected to graduate from his automotive engineering course with debts of between £15,000 and £20,000.
PA