The DVLA at Swansea is sending out warning letters to drivers as follows:
"In order to assist other motorists in identifying potentially dangerous
drivers, it's now compulsory for anyone with a lower than average driving
ability to display a warning flag
The flag (comprising of a red cross on a white background) will be attached
to the top of at least one door of their vehicle.
For drivers of exceptionally low ability, additional flags are required."