If you’re in London, campsites aren’t worth staying at. You end up spending more on travel into London than you save over staying in a backpacker hostel. Most campsites are at least 10 miles out, sometimes 15.
Best way to do London on the cheap is hostelling.
There are a few cheap youth hostels that’ll do you a room for £10-£12 (15-18 euros) a night, mainly near Kings Cross, like this one http://www.generatorhostels.com/london/
I hear they can be cool, mainly a bit party party so it depends on what you’re in town for.
If you buy an A-Z (map book) when you get there, you can get around easily, you don’t need to spend money on the tube, particularly if you’ve got a unicycle, central London is pretty small.
If you do need to use the tube or buses, buy an Oyster card from the ticket office at any tube station, this is a card that you top up like a mobile phone, and then pay for the tube with. The oyster card costs you £3 and saves you about £2 per tube journey if you’re doing short journeys in Zone 1 because you don’t have to buy the rip-off tourist tickets for the tube.
If you’re a trial / street riders or whatever, make sure not to miss the South Bank. This is the area on the south bank of the Thames, starting from the London Eye, and going East until Tower Bridge (a couple of miles or so), there’s always loads of skaters, trials bikes, bmxs etc. around there, it’s a cool place to ride, and where everyone goes for trials riding. (go to Waterloo station and ride East, or London Bridge and ride west)
There is sometimes a trials ride starting Sunday 10 at the Shell Centre (near Waterloo station), usually bikes there, but sometimes some unicycles.
Joe