What is Cat S?

Cat S stands for Category S (Structural). It's one of the insurance industry's write-off categories, used when a car has been damaged badly enough that its structure was affected - for example a bent or twisted chassis, or a crumple zone that's collapsed - but the damage has been assessed as repairable.

What it means for a buyer: a Cat S car can legally be repaired and driven again, but it's had a more serious history than a car that's never been written off. The quality of the repair matters enormously and isn't something you can judge from the outside - a professionally repaired Cat S car can be perfectly safe, while a poorly repaired one can hide real structural weaknesses. It's also very likely to be worth noticeably less than an equivalent car without a write-off history, both now and when you come to sell it.

This category, along with Cat N, replaced the older Cat C and Cat D system in October 2017, when the insurance industry updated the rules to focus more on structural safety rather than just repair cost.

Source: gov.uk: insurance write-offs