What is a Category N or S write-off — and is it safe to buy?

If a check comes back showing a car was written off, the first thing worth knowing is that "written off" doesn't automatically mean "wrecked and dangerous." Since 2017, UK insurers have used four categories — A, B, S and N — and two of them (S and N) describe cars that are legally allowed back on the road once repaired. This guide focuses on those two, since they're the ones you're most likely to come across and the ones people most often misunderstand.

What "Category S" and "Category N" actually mean

Category S (Structural) means the vehicle suffered damage that affected its structural integrity — a chassis, sill, or suspension mounting point, for example. It can be legally repaired and driven again, but the repair needs to be done properly, since structural work affects how the car behaves in a future accident.

Category N (Non-structural) means the damage didn't touch the structure — think a smashed bumper, a damaged interior from a break-in, or a flooded car with no structural harm. Cat N cars are generally simpler and cheaper to put right than Cat S.

Neither category legally requires the car to pass an independent engineer's inspection before it's driven again in England, Wales or Scotland — which is exactly why buyer caution matters more here than with almost any other check.

Why the category alone doesn't tell you enough

• The category tells you the type of damage, not the quality of the repair.
• Insurers write a car off based on repair cost versus its pre-accident value — a fairly minor bump on an older, lower-value car can trigger a Cat N marker even though the damage was cosmetic.
• A well-documented, professionally repaired Cat S car can be a perfectly reasonable buy at the right price. A poorly repaired one can be genuinely dangerous.

What to actually check before buying

• Ask for evidence of the repair — invoices, photos, and ideally an independent engineer's report, even though it's not a legal requirement.
• Get a proper inspection from a mechanic who isn't connected to the sale, specifically looking at the repaired area.
• Check the price reflects the write-off history — a Cat S or N car should sell for meaningfully less than an equivalent car with no accident history.
• Confirm your insurer will actually cover it, and get a quote before you commit — some insurers charge more, or decline outright, for a car with a write-off marker.

A write-off marker is a starting point for questions, not an automatic red flag or an automatic green light. Knowing which category you're dealing with — and asking for the paperwork to back it up — is what actually protects you.