I don't live in UK, and only visited a couple times, but it looks like CRR Luton is awfully close to you in Stevenage. They are highly regarded Leica techs.
Jaap suggested a IIIg. I've been intrigued by the IIIg myself, but only because I already have Ms. I find the flexibility to use both M and LTM lenses on an M body to be useful...its only LTM lenses on the IIIg.
Like me, you will probably not satisfy the Leica itch until it is an M model. Get whichever good condition M2, M4, M4-2, M4-P, M6, M6TTL comes your way. Any of these will be wonderful and all of them are the classic Leica M experience. I didn't suggest M3, M5, or M7 (or MP, digitals, etc): the M3 is wonderful but most of us want to use 35mm lenses at some point (yes, we all know about goggled lenses, but...), the M5 seems to be a great camera but its not the classic design -- you'll still be longing for a classic M. The M7 is also a great camera, but more electronic than mechanical and usually more expensive than my suggested models.
So I repeat: grab the first decent M2, M4, M4-2, M4-P, M6, or M6TTL you come across. For you, the differences among are marginal and not that important. FWIW, I love my M2, M3 and M6 just the same when they're working (a couple need repair). Heck, I've been enjoying my MDa recently; I just like how the M bodies feel in the hand.