The altered number plates a problem for the 'number plate recognition' computers linked into cameras on the motorways, fixed into cars and now in places such as car parks and even the eurostar.
Traffic police vehicles have cameras fitted which continuously scan the number plates of cars around them and cross check them against databases of tax + insurance.
On a useful side if you prebook parking at many major airports or prebook on the eurostar it reads your numberplate as your approach the barrier and has your information already displayed.
