Hi.
I'm currently having the same dilemma.
i'll be back in the UK for 10 days in June and will be spending a few days with friends just a few miles from Minispares main warehouse in Potters Bar.
Just can't think what I need/want and can also fit into luggage at the same time!
Hope you guys have a nice time in the UK.
minispares is definitely one of the most respected all round suppliers - they remanufacture a lot of parts themselves from the original tooling. Depends on where you are going but Potters Bar is just on the edge of London (north), near the M25/A1(M) junction.
http://www.minispares.com/
I think prices between most of the main suppliers only ever varies a little and not to the extent that it would be worth travelling a great distance to go to get something that was 2 pounds cheaper. There's always the odd exception, best to get a copy of MiniWorld or Mini magazine and have a browse.
Moss seem to have a lot of stuff that you don't tend to see in other places though (they've got a few shops i think, but the London one is in South West London
http://www.moss-europe.co.uk
Depending on when you are going, could be an idea to see if there are any mini shows on when you are there - it's summer time and the show season is underway. A lot of the time you can get stuff at a great discount from the stalls at the shows.
Most of the shows are in the countryside though, so you'll normally need a car to get there.
Post a question on
http://www.minifinity.com and you'll be sure to get some help/opinions/advice and also a list of events/runs and shows
PS noticed that this year's International Mini Meet is in Poland 2-4th June - backpacking taking you anywhere near there by any chance??