Mar 022011
 

A. If you are being contacted about fines or charges for which you are not responsible because someone else is using your registration mark, it is possible that your vehicle has been cloned. Cloning involves stealing a car and then giving it a convincing new identity… by copying the identity of a very similar (non-stolen) vehicle that’s already in use… sometimes in the local area, sometimes from across the country.

Criminals find an exact match of the car they have stolen (colour, year, model) and then copy the identity of the legitimate vehicle (number plates, other ID marks etc)  therefore making it appear legal, especially to security cameras or even a cursory inspection
http://www.direct.gov.uk/en/Motoring/VehicleCrime/DG_10020050