CAT S and CAT N Write-Offs Explained: Should You Buy One?
You've found a car at a price that seems too good to be true. You run a basic check and it comes back as a CAT N or CAT S write-off. The seller says it's fine, fully repaired, drives perfectly.
Should you walk away? Should you negotiate? What does it actually mean?
This guide covers everything you need to know about insurance write-off categories before you buy.
What is an insurance write-off?
When a car is involved in an accident, stolen and recovered, or damaged by flood or fire, the insurance company assesses whether it's worth repairing. If the cost of repair is close to or exceeds the car's market value, the insurer writes it off.
Written off doesn't necessarily mean the car is a crumpled wreck. It means the insurer decided the repair bill wasn't economically justified. The car gets taken off the owner, the insurer pays out, and the vehicle is assigned a category.
The four write-off categories
The most severe category. The car must be crushed entirely. Not a single part can be resold. If you ever see a Category A car being sold, it is illegal and almost certainly a scam.
The body shell must be destroyed but parts can be salvaged and resold. A Category B car should never appear as a complete, driveable vehicle on the market. If it does, walk away immediately.
The car has sustained structural damage, meaning the chassis or frame has been affected. It can legally be repaired and returned to the road, but it must be professionally assessed and repaired to a roadworthy standard. The seller must disclose it. The write-off marker stays on the vehicle permanently.
The car has sustained damage that doesn't affect the structural integrity of the chassis or frame. This could be cosmetic, electrical, or mechanical. It can be repaired and sold without the same level of structural concern as CAT S, but it still carries a permanent write-off marker and must be disclosed.
CAT S vs CAT N: what's the real difference?
The key distinction is structural integrity.
A CAT S car has had its chassis or frame damaged. Even after a professional repair, there are legitimate questions about whether it will perform as intended in a future accident. Crumple zones may not behave as designed. Alignment can be subtly off. These aren't hypothetical concerns.
A CAT N car has damage that doesn't touch the structural frame. A hard rear-end shunt that damages the boot, lights, and electrics but leaves the chassis untouched is a typical CAT N write-off. The structural concern is lower, but it's still a car with a history.
Neither is automatically a bad buy. But both require more scrutiny than a clean car.
Should you buy a CAT S or CAT N write-off?
Honestly, it depends.
The case for buying one:
A properly repaired write-off can be a genuine bargain. The write-off marker permanently reduces the car's value, which means you pay less for what may now be a fully roadworthy vehicle. For a second car, a high-mileage daily driver, or someone on a tight budget, the maths can work out.
The case against:
- Resale value is lower. When you come to sell, the write-off status will come up and suppress your price.
- Insurance can be more expensive or harder to arrange.
- A CAT S repair done badly is a genuine safety risk.
- You're relying entirely on the quality of the repair work, which you may not be able to verify.
The rule of thumb: CAT N with documented professional repair at a reasonable discount — possibly worth it. CAT S requires a specialist inspection before you commit to anything.
What to check before buying a write-off
Get the full repair history
Ask for the insurance repair documentation, garage invoices, and any post-repair inspection certificates. A reputable repairer will have provided these. No paperwork means no way to verify the quality of the work.
Get an independent inspection
For any CAT S car especially, pay for an independent inspection from a qualified mechanic or specialist. The AA and RAC both offer pre-purchase inspections. It costs around £100-200 and could save you from a serious problem.
Check the MOT history
The MOT history won't tell you directly that a car is a write-off, but it will show you the car's full timeline. A gap in tests around the time of the incident, followed by an MOT after the repair, gives you a timeline to cross-reference with what the seller tells you.
Don't Buy A Lemon shows this history automatically on every listing.
Check the write-off category using a vehicle history check
A basic HPI or free alternative check will confirm the write-off category. Don't rely on the seller's word alone. Check it independently.
Negotiate hard on price
A write-off marker permanently affects value. Factor in the cost of any remaining repairs, the reduced resale value, and the potential insurance premium increase. A CAT N at 20-25% below clean market value might be fair. A CAT S should be discounted more significantly.
How to tell if a seller is hiding a write-off
Some sellers don't disclose write-off status, either deliberately or because they genuinely don't know (for example if they bought the car without checking). Signs to watch for:
- Price noticeably below market value with no obvious explanation
- Seller is vague about the car's history or previous accidents
- Mismatched paint across panels
- Panel gaps that are uneven or inconsistent
- Evidence of heavy bodywork repairs (filler, overspray, disturbed seals)
- A gap in MOT records around a specific date
Always run a history check. Never rely on a seller's assurance alone.
Stop checking manually. Start browsing smarter.
If you're comparing multiple cars, running all the online checks manually on every listing takes time you don't have. Don't Buy A Lemon handles the MOT history and mileage check automatically on every car you browse, so you know the history before you've even messaged the seller.
Frequently asked questions
Is it legal to sell a CAT S or CAT N car? Yes, as long as it has been properly repaired and the seller discloses the write-off status. Failing to disclose it is fraudulent misrepresentation and gives you grounds for legal recourse.
Does a write-off affect insurance? Yes. Insurers treat write-offs differently. Some will refuse to cover a CAT S car entirely. Others will insure it but at a higher premium. Always declare write-off status when getting quotes.
Will a CAT N or CAT S car pass an MOT? Yes, if it has been properly repaired to a roadworthy standard. An MOT checks the car's current condition, not its history. A well-repaired write-off can pass an MOT just like any other car.
How do I find out if a car is a write-off? Run a vehicle history check. Services like HPI, Motoreasy, or CarVertical will show write-off status. The DVLA record will not show this, so don't rely on the free DVLA check alone.
What was CAT C and CAT D? The old categories before 2017. CAT C was equivalent to today's CAT S (structural) and CAT D to CAT N (non-structural). If you're looking at an older car, you may see these categories in its history instead.