Category A: Scrap only - this vehicle should have been crushed. It should never reappear on the road and there are no economically salvageable parts. It is of value only for scrap metal - e.g. a totally burnt-out vehicle.
Category B: The bodyshell should have been crushed. The vehicle should never reappear on the road, but it can be broken for spare parts plus any residual scrap metal.
Category C: Vehicle extensively damaged and insurer has decided not to repair. The vehicle should have an independent inspection before being allowed back onto the road.
Category D: Vehicle damaged and insurer has decided not to repair
It varies with Insurers whether they will cover them. Some will not cover CAT C/D's at all but
most will require a copy of MOT, engineers report and/or VIC test depending on the category of write off and the insurer.
Hope that helps