hmm
For british weather a wet suit is idea, Go in Skins and loose about 50 layers
I first started with a 3.2 last August and it was nice, this year I went in May and april and my 3.2 wasent cutting it so I bought a 5.4.
My friend got a 5.4 when we went in may for like 90 pounds which is good, you can find nice deals but I surppose anything over 4.8 is a dead cert.