Well they managed to eventually get my 'good' key, the one that came with he car working again, so what was looking like a potential nightmare was averted.
I rang round a couple of places and nobody could supply a transponder that would work. The chap at Hinkleys ran my reg no. through his database and said it had to be a factory order from VW as they come encrypted, although still requiring final coding at the garage.
So I ordered a new end unit (blade end of he fob) for £62 and they have agreed to do the coding for free...
To be honest, I didn't want the risk of losing the functionality of my one existing key..
I found out from the locksmith that cut my new key that the transponder was a virgin one anyway, so buying another was not a sure fire hit anyway.
Moral of the story - if someone is flogging a golf with only 1 key, it needs to be £200 cheaper. Oh, and don't lose your key!