After I messed up the brakes on my car once, I concluded that brakes are the one thing I don't want to do myself - I don't mind if the bike won't start because of my incompetence, but I really quite object to the bike not stopping because of the same problem!
If you're in N.E. London there's a really good little independent workshop / dealer on the A12 near Newbury Park station - they're quite good at changing brake pads!