Update 14 August - I am going on the Saturday - have bought ticket in advance using BOGOF -which is available until 23 August - so currently will have a spare ticket available at half price - if interested let me know . Tickets are £12 on the door on the day.

Megabus train has a return trip to London for £27 using advance purchases on specific trains (have gone with 9:32 arrives London 11:14 so should be at Olympia by 12:00 and then 18:15 back) - http://uk.megabus.com/

http://london.vegfest.co.uk/