I have to echo both Phil and Jock's comments-- shop carefully and shop wisely. From personal experience I can recommend Stewart Christie (but they are expensive) and Kyle Macpherson patronizes Kinloch Anderson in Leith (the sea port of Edinburgh) both of whom have an excellent reputation.

A truly bespoke jacket and waistcoat can run to GBP 1,000; made to measure will probably be half that, and off the peg you are probably going to spend around GBP350 for a quality jacket. For the average gentleman there is very little difference between made to measure or bespoke; both will fit extremely well and even with made to measure it is possible to somewhat customize the jacket-- things like buttons.

The major advantages to a bespoke jacket are in the wide selection of fabrics, buttons, lining--- every detail can specified to your exact requirement (my dinner jacket is lined in silk Macmillan Hunting tartan, for example). One other advantage is that bespoke garments make one watch their waistline... No one wants to out grow a GBP 1,000 kilt jacket!