The guy I was talking to couldn't sort it and so he passed me to 2nd level.
I was on the phone to that guy for around an hour and he finally sorted it for me.
He sent me an email and it came straight through. He then tried sending the verification mail and it didn't appear. Finally, he managed to get the iPhone to synch with iCloud by resetting the password - something that I had already tried twice before.
He very kindly gave me his direct email at apple so that I could get in touch with him if anything else caused problems or if I remembered something after we had ended the call.
An absolute star - thank you Andrew - sevice above and beyond. Pity I can't let your line manager know how happy I am after your time and trouble. My 3GS will now synch to iCloud.
@fromsouth - many thanks for your suggestions and taking the time to reply. It was doing my head in becasue nothing I seemed to do made any difference.
gp : )