I posted an update as I was asked on 29th Mar what the latest news was. I am not panicking any more, nothing has escalated as far as I know, so it is all to me a matter of mild irritation of having to walk down to the post box to return the letter.

I am not forcing anyone to read the thread, and it may be useful if this happens to someone else in the future, and I would kind of like to know how two different police forces got my address when the licencing authority have stated categorically that the vehicle is not registered at my address so there is an on going data protection issue which I would like to have resolved too as there is a duty of care which owners of databases should be adhering to.