Scroll any car marketplace and you'll see them: cars thousands of pounds under market value with three little letters in the description — Cat S or Cat N. Some are genuine bargains. Some are structural nightmares wearing fresh paint. Here's how to tell the difference.

What the Categories Mean

When an insurer decides a damaged car isn't economical to repair, it's "written off" and given a category:

• Cat A — Scrap. The whole car must be crushed. Can never legally return to the road
• Cat B — Break. The body shell must be destroyed; parts can be salvaged. Never road-legal again
• Cat S — Structural. Damage to the structure (chassis legs, crumple zones). Can be repaired and returned to the road
• Cat N — Non-structural. The structure is untouched — think doors, bumpers, lights, electrics, interior. Can be repaired and returned to the road

Older listings may say Cat C or Cat D — the pre-2017 system, roughly equivalent to S and N respectively. A key nuance: "non-structural" doesn't mean "minor". A flood-damaged car with ruined electrics is Cat N. So is one with a £4,000 bill for panels and airbags.

Why Cheap Cars Get Written Off

Repair costs are judged against the car's value. A £2,500 bumper-and-wing repair writes off a £4,000 Fiesta but barely registers on a £30,000 BMW. That's why plenty of written-off cars had damage that was, in absolute terms, modest — and why the used market is full of perfectly serviceable repaired examples.

The Real Costs of Buying One

• Discount: expect 20–40% below an equivalent clean car. Cat S sits at the deeper end, Cat N the shallower. If a write-off is priced like a clean car, walk away — you're taking all the downside for none of the saving
• Insurance: most insurers cover write-offs, but some load the premium or refuse; declare it or risk a voided policy. Payouts after a future claim will also reflect the reduced value
• Resale: the marker follows the car forever. You bought at a discount; you'll sell at one too, to a smaller pool of buyers
• Finance: some lenders won't finance Cat S cars, which shrinks your future buyer pool further

How to Check a Write-Off Properly

1. Get the repair evidence. A reputable repairer provides photos of the damage and invoices for parts. "Professionally repaired, no photos" is a red flag, especially on a Cat S
2. Read the MOT history around the incident. The damage date usually shows up as a gap in testing or a sudden garage change. What matters is what comes after: fresh suspension, steering or tyre-wear advisories following the repair suggest the geometry never came back right
3. Pay for an HPI-style check. Free checks won't reliably show write-off markers — this is one of the few times the £10–£20 paid check is non-negotiable. It also covers outstanding finance
4. Get an independent inspection on Cat S. Structural repair quality is invisible to a test drive. £100–£200 for an engineer's once-over is cheap against a misaligned shell

The Verdict

Cat N can be a smart buy if the damage is documented, the repair is invoiced, and the discount is real — especially for a car you plan to keep long-term, where the resale penalty matters less.

Cat S is for confident buyers only. The discount is bigger for a reason. Without repair photos, invoices and ideally an independent inspection, assume the worst.

And if the seller doesn't mention the category at all but the price looks too good? That's not a bargain, that's a trap — one of several we cover in Red Flags When Buying a Used Car.