Thank you - this problem has now been solved!
However the reason for it may be of interest to other users - I found the TomTom Customber service email to be absolutely useless, but a phone call to Customer Services sorted it out.
The problem was that, due to software error at TomTom, my account contained errors and the effect of this was that it failed to offer the correct map - it was offering maps which were not valid for my device, and that is why I got the activation problem.
The very helpful guy on the phone line realised this as soon as I explained the problem; he then deleted and reinstalled my TomTom account and this has completely solved the problem - my new map simply works - no activation, no nothing.