cat C usually is worse accident damage than cat D, but for older classic many are getting cat C to write them off, look at copart.co.uk selling most insurance accident damaged cars some cat C is not very much damaged and even cat D with just a light scratch.
the worst is CAT B (breaker) only people with breaking license can purchase, the dvla allow appeals on cat b to be allowed back on the road. i am presently in afight like thAT FOR 2014 sl400 which runs and drive being sold as a breaker!!!
cat C need mot and VIC check Vechicle Identity CHeck) to confirm this is the original car not cloned etc before logbook reissued back by dvla
for all who are interested if your car get damaged and it is not your fault contact i refer to people who claim direct from the other person insurance so firstly accident remain unrecorded on your car, and thus no increase in future premium
i hope it helps