Slaters
http://www.slaters.co.uk/stores/
In house tailors and a range starting at £50 upwards to ££££.
Free Tailoring for the life of the product too, so if big Tone ends up not so big, they will take the jacket in for you FOC.
You wouldn't catch me buying a suit from slaters..... you'd look like your on work experience 
I'm an odd shape to fit for, and have never had a bad suit from Slaters. I have from many other places on the high street.
In terms of fit vs. cost, you can't really go wrong with it.
The key is to be fitted by one of the older guys. Who'll tell you if something looks crap on you.