Obtaining a bike temporarily!

Hello

Having started tri's on a trial basis this year, and enjoying it hugely, I'm planning to sign up for IMCH 2009 and will be buying gear later this year.

In August this year I'm doing London Tri, and it's become very apparent that whatever I do on my hybrid bike, I'll be left in the dust by racing bikes. I don't have the money at the moment to buy a decent racing bike that will do for 2008 and 2009, and I don't want to spend money (I don't have) unnecessarily now for one or two events this summer.

Shall I bite the bullet, do London on a hybrid and save up for a good bike for next year, or could anybody tell me of anywhere that rents road bikes on a short term basis? I'm in London btw.

 Many thanks