In reply to gethin_allen:
I have an old "D" bike lock with a flat key (rather than one of the round types) and couldn't find anywhere on the high street that had a suitable master to cut a spare from. However, the Timpsons head office in Wythenshawe, Manchester has a special machine which I belive can cut just about anything.
I only live about 15 miles from there so called in when in the area and they were able to cut me a spare although I had to leave it with them for a few days and it cost about £15.
Anyway, you could try contacting them and seeing if you could post your original to them to see what they can do?
http://www.timpson.co.uk/page/109/contact