Protesters have attacked a police van as crowds swelled during angry demonstrations against rising university tuition fees.
A group of young men leapt on to the roof, smashed the windscreen, daubed it with a slogan and hurled sticks at the vehicle which was parked in the middle of Whitehall, central London.
The mob surrounded the Metropolitan Police van close to the Foreign and Commonwealth Office, where they pulled off wing mirrors and daubed it with graffiti.
A handful of young women could be seen attempting to stop further damage as a man urinated on one front wheel.
Witnesses said a smoke bomb was thrown inside the van as protesters, some covering their faces with scarves, hit the windows with wooden sticks.
Several fireworks were let off nearby, greeted by cheers and whistles, as a light was smashed on the back of the vehicle.
The van was abandoned a short distance from the Royal United Services Institute (RUSI) where Met boss Sir Paul Stephenson has been giving a speech on terrorism.
In other areas of Whitehall there was a party atmosphere, with students jumping up and down to dance music as helicopters hovered overhead.
The protest has been dubbed Day X, with parents, teachers and trade unionists invited to join students.
Many of the rallies have been organised by the Education Activist Network and the campaign group Youth Fight For Jobs.