Show the key shape, it's likely it is from an existing padlock range, so any key cutter, from what you can see looks like it could be abloy pattern? semi circular with cut outs? Key cutters have a huge catalogue of shapes and types of keys they can copy
Neil, we did take the key into our local branch of Timpsons and the guy behind the counter took one look at the key and said "Sorry, can't do that one." I have since found out from the Timpsons web site that
"We have our own internal key excellence centre based in Manchester. If our branch colleagues are stumped, they can call our helpline and talk to someone who specialises in unusual keys. The helpline helps out over 1000 times a week." so I will be contacting 'em again.
You're right, the key is a half-round one. Will post a piccy up later.