I know the CAT isn't the point of the post and the OP's question. However, if OP bought the car at auction, was it a private entry, or direct from the insurer? If a private entry, there's no shortage of backstreet cowboys who will fix up the majority of damage, then push the car through auction with half the damage repaired. No matter where it is on the body, damage as light as a ding, or even a good whack, can't possibly write off a £55k car.
Then again, we all remember my Cat B flood damaged BMW post.