People weeing off roof. After being pushed back a few students ran around the building to try another exit. More police have turned up. General feeling that this is a widespread protest involving many people that would not normally come out to protest.
Early suggestions say this will run front page of Guardian.
Estimates now say 52,000 on protest
Update: Protesters are now spraying a hosepipe at the building. There is graffiti sprayed across the walls. The bonfire is still burning.