I was looking at this the other day...
There must of been more damage than just "the bumper being ripped off" for it to be cat D surely?
To start with who is going to advertise a CAT D as 'stuffed in back end, twisted chassis, damaged floor pan' etc etc
Of course there was more damage but you have to use you head.
Recovery and storage after the accident say £750ish (Mine was £440 for recovery & 2 days storage)
New bumper from renault £200ish
Respray rear bumper £250ish
If its been 'ripped' off then no doubt the mounts will require a bit of work to get it to line up correctly and maybe pulling out £200
Due to nature of bumper being 'ripped' off there may be slight damage to the rear 1/4's say £100 a side to tidy up £200ish
Just that alone is (£1600) almost 50% of the book value so is almost BER to an insurance company hence the CAT D
It does not take much in this day and age to write a car off.
If I was going to buy a CAT C or D I would not even contemplate buying one without a documented history of its repair and it must have pre repair pictures so I can make my own judgement.