another vote for Marks and spencers... also- i bought a Ben sherman suit from Debenhams, and one of the legs was a whole inch wider than the other, ( so i obv sent it back).... M&S is deffo one of the best places ive found, for quality, value and choice. (from all the next suits ive seen in various stores, the QC seems to be lacking)
Slaters is good also, but from what i saw, a slightly older style of suits, but ofcourse the customer service is brill and they adjust FOC for life of the suit.