Current Categories
At the moment cars will fall either within Category C or D depending on the cost of repair in relation to their pre-accident value. Often, when you add the costs of hire car provision and other expenses to the insurers costs, a low-value car will quickly become more expensive to put back on the road than to write-off as a Cat C. Costs become a real problem if sourcing parts for your car is tricky and time-consuming - as many Jaguar owners can find - as insurers don't want the responsibility of these extra costs.
The result is that some relatively low-value cars, such as an everyday classic Jaguar, can be classified as a Category C despite having very little damage and having many more good miles to run, for a relatively minor repair.
The Future Post 1 October 2017
To try and address this ongoing problem, two new Categories of S for Structurally damaged repairable and N, non-structurally damaged repairable, will come into being on 1 October, replacing both Category C & D.
For example, cars with minor damage (perhaps from attempted theft or vandalism) and a low pre-accident value will be categorised as Cat N (non-structurally damaged repairable) rather than Cat C, allowing it to be repaired with second-hand parts and returned to the road.
Cars with more significant structural damage, from a traffic accident for example, will be Categorised as Cat S. This allows it to be repaired but also tells any future owner that there has been structural damage in the past. This category is relevant whether the car has a high or low pre-accident value.
Category A & B will remain after 1 October. Cat A means the car has no salvageable parts and should be scrapped and Cat B cars can be broken but are too badly damaged to be repaired safely.
Read more at the ABI Website