Just found this:
Vehicles are assigned "Q" prefix registration numbers to show that their origins or age are uncertain. "Q" numbers are therefore non-transferable and must remain with the vehicle unless documentary evidence which confirms its origins or age comes to the attention of the DVLA who may then choose to assign an age-related registration mark. If you find such documentary evidence for your Q plated vehicle then you should send it to your nearest DVLA Local Office who may then assign a replacement age-related registration number plate to the vehicle.
