If you're shopping for a used car, you'll occasionally see vehicles listed as "Cat N" or "Cat S" — often at significantly lower prices than similar models. These labels mean the car has been written off by an insurance company at some point in its history.
Here's what each category means, whether it's safe to buy one, and what checks you should do first.
The four write-off categories
The UK uses four insurance write-off categories, introduced in October 2017 to replace the old A, B, C, D system:
Cat A — Scrap only
The vehicle must be crushed entirely. No parts can be salvaged or reused. This is reserved for the most severely damaged vehicles where even individual components could be dangerous. You will never see a Cat A vehicle for sale — they are destroyed completely.
Cat B — Body shell must be crushed
The body shell must be destroyed, but undamaged parts can be removed and sold separately. Engines, gearboxes, and other mechanical components can be salvaged. The vehicle itself can never be driven on the road again.
Cat S — Structural damage (repairable)
The vehicle has suffered structural damage — to the chassis, frame, or structural elements of the body. It can be repaired and returned to the road, but the repair must address the structural issue, and the vehicle must pass a new MOT before being re-registered.
Cat S replaced the old "Cat C" category. The key distinction is that the damage affected the vehicle's structural integrity.
Cat N — Non-structural damage (repairable)
The vehicle has suffered non-structural damage — body panels, bumpers, lights, interior, electrical components, or mechanical parts, but not the chassis or structural elements. It can be repaired and returned to the road.
Cat N replaced the old "Cat D" category. These are often cosmetically damaged vehicles where the repair cost exceeded the insurer's threshold (typically 50–60% of the vehicle's value), even though the damage itself may be relatively minor.
Why do cars get written off?
An insurance company writes off a vehicle when the cost of repair exceeds a certain percentage of the car's market value. This threshold varies between insurers but is typically around 50–60%.
This means a £3,000 car with £1,800 of damage will likely be written off, even though the damage may be straightforward to repair. The insurer pays out the market value to the policyholder and takes ownership of the vehicle.
The result is that many written-off cars — especially Cat N vehicles — have perfectly repairable damage. Some have very minor issues: a cracked bumper, a dented door, or a faulty airbag warning light. The "write-off" label reflects an economic decision by the insurer, not necessarily the severity of the damage.
Can you buy a Cat N or Cat S car?
Yes, and many people do. Written-off cars are typically sold at auction or through salvage dealers, often at 30–50% below their pre-damage market value. For a buyer who knows what to look for, they can represent genuine value.
However, there are important risks:
Risks of buying Cat S
- Structural damage may not have been properly repaired — Even if the car looks fine, hidden issues with the chassis or frame can compromise safety in a future accident.
- Alignment problems — Structural repairs often affect wheel alignment, panel gaps, and how the car drives. These can be difficult and expensive to fix properly.
- Future resale value — Cat S vehicles are always worth less than equivalent clean-history cars. The marker is permanent and shows up on any vehicle history check.
Risks of buying Cat N
- Repair quality varies enormously — Some Cat N repairs are done to a high standard by professional body shops. Others are bodged together with cheap parts to maximise profit.
- Electrical damage — Flood-damaged cars are often categorised as Cat N (non-structural), but water damage to electrical systems can cause persistent, hard-to-diagnose faults for years.
- Resale impact — Like Cat S, the Cat N marker is permanent. Expect to sell for 20–30% less than a clean-history equivalent.
What to check before buying a written-off car
1. Run a vehicle check
Start with a free car check to verify the vehicle details, MOT history, and mileage. Look at the MOT history carefully — were there any failures or advisories after the write-off date that might indicate poor repair quality?
2. Get a paid history check
A paid HPI or AA check will confirm the write-off category and date. Free checks cannot access insurance write-off data, so this is essential for any car where you suspect or know about a write-off history.
3. Get an independent inspection
For Cat S vehicles especially, pay for an independent vehicle inspection from the AA, RAC, or an independent engineer. They will check the structural integrity, alignment, panel gaps, and overall repair quality. This typically costs £100–£200 and is well worth the investment.
4. Ask for repair documentation
A reputable seller should be able to show you invoices, photos, and documentation of the repair work. This should detail what was damaged, what was repaired or replaced, and who did the work. Be wary of sellers who cannot provide this.
5. Check the MOT history
Use our MOT history check to see whether the vehicle passed its post-repair MOT cleanly, and whether any advisories have appeared since. Recurring advisories on suspension, steering, or alignment could point to a structural repair that wasn't done properly.
6. Inspect thoroughly
Look for:
- Uneven panel gaps — Doors, bonnet, and boot should line up evenly
- Mismatched paint — Check in daylight from different angles
- Welding marks — Feel under the wheel arches and along seams
- Fresh underseal — Can be used to hide structural repairs
- Tyre wear patterns — Uneven wear suggests alignment issues
Does a write-off affect insurance?
Yes. Insuring a previously written-off car typically costs more, and some insurers won't cover Cat S vehicles at all. Always get insurance quotes before committing to a purchase.
The vehicle's agreed value for insurance purposes will also be lower than an equivalent car with a clean history, which means you'll receive less if the car is written off again.
The bottom line
Cat N and Cat S cars can be genuine bargains, but they come with risks that require extra due diligence. The write-off marker is permanent and will always affect resale value. Our car valuation guide explains what factors influence what buyers will pay.
If you're considering a written-off car, start with a free car check to review the full vehicle history and MOT records. Then invest in a paid history check and an independent inspection. The extra £200–£300 spent on checks is a fraction of the potential cost of buying a poorly repaired vehicle.