As finding an accomodation for event can be a nightmare, here is the address of a student halls close to the competition area and where you will be able to book some bedrooms for one or two nights.

Mana Ash house (student halls)
It is situated close to the event, near Southwark station.
They are flats of 6/7 rooms with a comunal kitchen.
Price per room per night : £19.50.
Contact number : 0207 841 0486 (for group bookings)
For individual bookings : http://www.summerbreaks.org (Name of the house : Mana Ash House)

Book as soon as possible, the rooms may go very quickly.