Well I may just have finally got my code.
It was simple really. Didn't need to remove the unit or mess around with seriel numbers etc. I simply looked in the owners handbook for the original supplying dealer, a company in Leeds, and called them up.
I was put through to the parts department, they asked for the reg number, and they had a record of the radio code. Simple!
Hope this helps others in the same predicament.
Course I have to wait an hour now with the ignition switched on so that I can enter the code.