I have seen the same but the cars I have seen them on have been Isle of man plates I think...red badge with 3 legged person or something..mind you the cars were a bentley GT and a nissan GTR with the same plates. Rich git.
Its not possible, a single number plate can only be on one vehicle at any one time, it could just be that they have doctored the plate to make it look the same, eg a D made to look like an O...etc etc....
Im sorry guys but I'm with Wai-Fan here. I have 100% seen it on 2 cars and I seem to come across it everyday as the guy always parks same place. Isle of man plates so there must be a different rule for them unless its classed as trade plates or something? I seen the bentley and gtr constantly switched.
Here is a photo with two cars with the same registration - H5DJR. One is my 2007 Sportback which I was trading in and the other was my new 2009 Sportback which I was collecting the following day. The dealer organises the transfer of the plate. Not strictly legal as the 2007 Sportback had, by this time, been given a replacement registration number but I leave it the dealer to prepare and fix the new plates.