I have been using Bitbargain but not happy enough so far.
Bitbargain -- Difficult to be a seller thus the market is asymmetrically biased
Localbitcoin -- Not exchange
Although you should be better change GBP to USD (not EUR) and buy somewhere else, I would say coinfloor is the best UK exchange if you stick to domestic one as of now.
Trading volume is above 50 btc and much better than two above.