This is the actual position with regard to Cat D cars: they are simply cars which are uneconomical for an insurance company to repair. Insurance companies are obliged by their terms to restore the insured to the position they were in before the accident, so they are obliged to use new, manufactures' components in repairs. In addition, they provide new cars as similar as possible as courtesy cars. My 18 year old son recently had his Corsa hit by a driver who admitted liability. My son only has 3rd party on his Corsa due to cost. The Corsa cost £4k second hand 3 months ago. He has been supplied with a brand new Corsa while negotiations/repairs carried out. His damaged car was driven to a repair facility. I spoke to the engineer assessor today. He said the actual cost of repairing the car would be about £1k.However, they were obliged to get an estimate from a Vauxhall approved repair centre (£3k), pay for his courtesy car while repairs were carried out(£1k), which exceeded 66% of the value of the car (66% is the agreed write-off figure in the insurance industry).To cut their costs, they offered me £4k, or the car for £500 plus £3.5k.I phoned my sons insurance company, they had no problems with keeping the car on his insurance, and confirmed his (non-existent at the moment) NCB would be unaffected. So we get the car back, plus £2.5k after repairs. The only reason Cat D cars are hard to sell is because buyers do not realise what Cat D means (It just means uneconomical to repair).People think "insurance write-off" means mechanical damage- it does not. Cats A, B and C relates to these cars, and they are not offered for sale. Hope this info helps.