VCAR = Vehicle Condition Alert Register
In short the vehicle has been subject to an insurance 'write off'. Could be as minor as a stolen/recovered or as serious as a complete mangling.
There are Categories A-D, a search of the forum will explain which is which.
The downsides are that dealers will be unwilling to take it in future p/x and private buyers will run a mile.
Upsides, the possibilities of a bargain if you plan on never selling the car.