VCAR or V-car (Vehicle Condition Alert Register) is a database used by accident service and insurance companies in the United Kingdom. It is a list of vehicles that have been reported as being in an accident that caused damage. "V-car registered" may mean the vehicle is on this list.
Vehicles are listed on VCAR specifically when they were damaged badly enough for the insurer to classify them as a write-off. A vehicle that is on the VCAR list likely suffered serious damage from an accident at some point in its life. Some cars on the V-car register can legally be returned to the road and may have been repaired to a safe condition, but their presence on the list means further diligence about their condition is prudent.