Geektastic:
In the UK the fine is issued in the first instance to the person to whom the vehicle is registered.
If that person was not the driver, there is a legal form on the fine notice which they sign and have to give the name of the driver if it was not them. The fine is then re-issued to that person. If they dispute it, then off to the Magistrate's Court you go and the fines go up automatically for the person found to have been speeding, as do the points. With an additional charge of suppling false information if you lied on the form....
That is similar to here in Queensland (and most of the rest of Australia). You get the fine, and you can either "redirect" the fine (by filling in a Statutory Declaration), pay the fine, or contest the fine in court. You can't contest by writing a letter though, it has to be in front of a judge, which I assume is because of the way the whole system works.