In the UK, plates go with your car, not with you.
An example of this was shown on the show "Top Gear" when the hosts had to explain that one of the cars they bought to use in a special in Argentina had it's plates since it's manufacture. The plates were thought to be a reference to the Falkland Islands War and some local Argentinians basically rioted and tried to destroy the cars when Top Gear came through an area. From that, I took that plates generally stick with the car through the life of the car, regardless of owner.
For our UK friends: Here in the US, we go down to a local office to register our cars and get our plates then. When buying from a dealership, you generally get temporary plates to drive home (they can be good for up to 30 days, depending on the state) so that you can then do whatever you need to do at the local DMV or town hall to get your 'permanent' plates.