Up to 20,000 demonstrators are marching on the Houses of Parliament in London as MPs debate whether to triple university fees in England.
It is an issue which has already provoked violence at earlier student protests in London.
It also puts Deputy Prime Minister Nick Clegg in an uncomfortable position.
Before becoming junior coalition partners he, like other fellow Liberal Democrat candidates, signed a pledge to oppose any rise in fees.
So it could trigger an embarrassing backlash from within the governing coalition when MPs vote later.
The LibDem deputy leader has already said he will not vote for the increase.
Those against raising tuition fees to nearly 12-thousand euros say the rise will put a full education beyond the reach of many, and will saddle those who do go to university with long-term debt.
The government says with a monster budget deficit and a faltering economy the rise is a painful necessity.