Cat A, B, S and N: What a Written-Off Car Actually Means Before You Buy One

There are four write-off categories under the insurance industry’s salvage code: A, B, S and N. Cars in the first two can never legally return to the road, while cars in the second two can once they have been repaired. The letter describes the damage a car suffered before anyone worked on it, not how well it was put back together afterwards. And one of the two repairable categories does not reach the paperwork the way the other does, so it can be missing from the documents a seller hands across.

Key takeaways:

• Cat A and Cat B cars cannot return to the road. Cat S and Cat N can, once repaired.
• The marker is permanent, follows the car through every sale, and reduces what it is worth.
• The category is assigned before repair, so it tells you what was damaged rather than what state the car is in now.

Who Decides, and What a Write-Off Actually Is

A write-off is two decisions, one after the other. The first is commercial: the insurer decides it will not pay for a repair. The second is technical: a qualified assessor decides what kind of damage the car has suffered, and that second decision is the one that stays with the car for the rest of its life.

The Decision Is Economic Before It Is Technical

An insurer writes a car off when it chooses not to repair it. It sets the repair estimate against the car’s value immediately before the accident, and when the sums do not work, it pays the owner the car’s current value instead of the cost of fixing it.

That makes the age and value of the car as important as the damage. A repair bill that a new car absorbs without question can be uneconomic on a ten-year-old hatchback, so an older, cheaper car can be written off after damage that a newer one would have had repaired under the policy.

Safety comes into it as well. The industry code describes a catastrophically damaged vehicle as one that cannot be safely repaired to accepted industry standards, including cases where the manufacturer’s repair methods or parts are unavailable, or where previous substandard repairs or heavy corrosion are present.

The result is that two cars with identical damage can end up with different histories. One is repaired and carries no marker. The other is written off and carries a letter for good. The letter records that an insurer declined to pay for the repair, and what kind of damage it found when it made that choice.

The Code Behind the Letters

The categories come from the Association of British Insurers’ Code of Practice for the Categorisation of Motorised Vehicle Salvage. It is a voluntary industry code rather than law. The ABI says it created the code to fill the gap left by the absence of any regulation on written-off vehicles, and that all its member motor insurers support it and follow it. The ABI has called for the code to be put on a statutory footing.

The current version is Version 12, dated March 2025 and published on 28 May 2025. It replaced Version 11 from November 2019. The 2025 update brought electric and hybrid vehicles within the guidance for the first time, and added provisions for megacasting, the large single-piece castings now used in some car bodies, along with reusable parts and other modern construction methods. It also improved the wording for heavy goods vehicles and motorcycles.

The categorising is done by what the code calls an Appropriately Qualified Person. That means someone with a technical education and training record in vehicle repair, who holds a current competency-based assessment in salvage categorisation from the Institute of Automotive Engineer Assessors or an equivalent body. Each one is identifiable by a unique competency number.

Every categorised vehicle is entered on the Motor Insurance Anti-Fraud and Theft Register, known as MIAFTR. Under the code, that entry is how insurers meet their legal duty to notify the DVLA. The same notifications pass to vehicle data agencies, which is where paid vehicle history checks find the marker.

The Four Categories

The salvage code works through four questions in a fixed order. Is the damage serious enough for the code to apply at all? Is the car suitable for repair? Should any parts be reused? Is the damage structural? The answers produce one of four letters.

A car with little or no damage can fall outside the code entirely. Any car with structural damage cannot, and the code requires every one of them to be categorised.

Category A, Scrap

A Category A vehicle has been judged unsuitable for repair in its entirety. It is crushed once it has been depolluted and any recyclable material removed, and its registration document is never reissued.

The code lists the kinds of damage that lead to a car being crushed whole rather than broken for parts: fire damage that contaminates or cooks the components, water damage, chemical or biological contamination, or a request from the police. A Cat A car is one where nothing is judged fit to go back into another vehicle.

Electric cars get their own instructions. Where the high voltage battery can be removed safely, it is taken out and recycled separately. Where it cannot, as in a severe fire, it is recycled with the rest of the car.

A Cat A car offered for sale as a complete vehicle is a serious warning sign. The identity on its paperwork belongs to something that should no longer exist, and the only sound response is to walk away.

Category B, Break

A Category B vehicle has a structure that cannot be repaired. The body shell or chassis carrying the vehicle identification number is crushed, and the registration document is never reissued. Usable parts can be removed and sold on, which surprises a good many people: the car can never return to the road, but its engine, gearbox, doors and panels legally can.

There are firm limits. The code bars airbags, seatbelts, seatbelt pretensioners, seatbelt stalks and buckles from ever being resold or reused, whatever condition they appear to be in. Other safety-related parts can only be reused after checking against the manufacturer’s repair information, and only if they are undamaged and can be warranted.

Category B also catches cars that could in theory be repaired but cannot be done properly. Where new original structural components are not available, the code says the car must never be classed as repairable, and second-hand structural parts must not be used to justify a repair. On an electric car, the high voltage battery from a Cat B vehicle is assessed and either recycled or reused if it can be warranted.

Category S, Structurally Damaged Repairable

A Category S vehicle is repairable but has damage to some part of its structure or chassis. The code counts damage as structural if any structural element needs repairing, realigning to its original dimensions or replacing. Cosmetic repairs that involve no realignment are excluded.

The structural list in the code covers the parts that hold a car’s shape in a collision: the front bulkhead, the header rails above the windscreen and rear window, the roof side rails, the inner reinforcements of the A and B pillars, the inner sills, the front and rear chassis legs, the inner wings and wheel arches, and the rear back panel. The 2025 version adds the front and rear one-piece mega and giga castings used on newer cars.

Electric cars are where the 2025 update counts most for this category. On some electric cars the high voltage battery forms the floor of the car, or the floor depends on it for its strength. The code says that where a structural battery is damaged, the car must be classed as Category S.

The code expects structural repairs to follow the manufacturer’s methods or recognised researched repair methods, using new original structural parts. Restoring a car’s structure to its original dimensions takes measuring equipment and manufacturer data, not a pulling jig in a back yard. The code’s involvement ends at the category, though. It does not inspect the repair that follows.

Category N, Non-Structurally Damaged Repairable

A Category N vehicle is repairable and has no damage to its structure or chassis. The code itself adds that there can still be safety-critical items needing replacement, and that is the line most write-ups leave out.

Cat N does not mean cosmetic, and treating it as cosmetic is the most common error on this subject. The code’s non-structural list includes the bumpers and their reinforcements, the bonnet, front wings, slam panel, doors, rear quarter panels, roof panel, boot floor and tailgate. A frontal impact that fires the airbags and seatbelt pretensioners can leave the structure untouched and still be Cat N, with the systems the car relies on in its next crash all needing replacement.

Water and fire damage can land here too. A car with water in the cabin that has not reached a level compromising its electrical and safety components is categorised N, while deeper flooding pushes it to B. A car with fire damage that has not reached the structure can also be Cat N.

For electric cars, the code allows Category N only where any damaged high voltage battery is non-structural, and notes that the high voltage systems, battery included, can be compromised in a Cat N car. Some manufacturers deem their batteries unrepairable, and the code says any repair to a battery that can be repaired needs an expert such as a qualified high voltage technician.

What the Category Means for the Paperwork

This is where the two repairable categories part company, and where buyers get caught out. Both are recorded centrally. Only one of them reliably shows on the document a seller passes across the bonnet.

The DVLA, the V5C and Re-registration

When a car is written off, GOV.UK’s guidance on insurance write-offs tells the owner to send the V5C registration document to the insurer, keeping the yellow section for the motor trade, and to tell the DVLA. An owner who does not tell the DVLA can be fined £1,000.

An owner who keeps a Cat S car has to send the complete log book to the insurer and apply for a free duplicate using form V62. The DVLA records the category in the new log book. The industry code’s flowchart says the same thing: a Cat S car gets a reissued V5C carrying a note of its status.

Cat N works differently. GOV.UK says the owner can keep the existing log book. Where the code provides for a reissued V5C on a Cat N car, it specifies no note of the write-off. A repaired Cat N car can change hands with a registration document that says nothing about its history.

The write-off has not disappeared. The insurer’s MIAFTR entry still counts as the notification to the DVLA, and it still reaches the vehicle data agencies, so a Cat N car shows its marker on a paid vehicle history check. What it does not show is a letter on the log book, and that difference is the single most useful thing a buyer can know.

Why the Marker Never Goes Away

The code says MIAFTR entries for all previous accidents must be retained, and that entries are not modified or removed other than to correct errors. Re-categorisation is reserved for exceptional circumstances. A good repair does not remove a marker, and nor does time.

The record follows the car through every sale. Each new owner buys it with the marker and sells it with the marker, and it takes money off the price every time it changes hands.

Dealers face stricter consumer protection rules than private sellers, and a private sale leaves a buyer with far less comeback if something turns out to have been left unsaid. With a Cat N log book able to look untouched, a private seller can hand over clean-looking paperwork without volunteering a word about the write-off.

That makes the paid vehicle history check the only dependable way to find a write-off marker, and the time to run it is before any money moves. A log book that says nothing, alongside a history check showing Cat N that the seller never mentioned, tells a buyer something about the sale and the car alike.

Cat C and Cat D, the Old Letters

Cars written off before 1 October 2017 carry the old markers, and those still appear on history checks today. The old scheme ran A, B, C and D, with A and B broadly matching the current categories.

Cat C corresponds broadly to today’s S, and Cat D to today’s N. The important difference is the basis. The old letters were set by the cost of repair against the car’s value, while the current ones are set by the type of damage.

That means an old letter says less about what was broken. A Cat D car could have had structural damage that happened to be cheap to put right, and a Cat C car could have had none at all. Reading the old letters as if they were S and N gives only a rough guide, and the repair evidence carries more weight on a pre-2017 write-off than on a newer one.

Buying a Repaired Write-Off

The letter on a car’s record describes the damage it suffered, not the repair that followed. Buyers tend to treat it as though it describes the car in front of them. Whether a repaired write-off is a sound purchase rests on the quality of that repair, and the category alone cannot tell you.

What It Does to the Price and the Insurance

A repaired write-off typically sells at a substantial discount to an equivalent car with a clean history. The size of the gap varies with the category, the car and the quality of the documentation, and no reliable single figure applies across the market.

The discount works in both directions. A buyer who pays less going in will sell for less coming out, and the car will usually take longer to sell, as every future buyer meets the same marker and asks the same questions.

Insurance is the other cost. Some insurers decline repaired write-offs altogether, and others cover them at a higher premium. Getting quotes before committing to a car avoids discovering the problem after the money has gone, and the category should always be declared when arranging cover.

The Checks That Decide It

Start with a paid vehicle history check to confirm the category and the date of the write-off. Then ask the seller why the car was written off and what was damaged, and compare the answer with the category.

Ask for the repair evidence: invoices for parts and labour, photographs of the damage before repair and of the finished work, and the name of the garage or bodyshop that carried it out. Look specifically for invoices showing new airbags and seatbelts, as the code bars salvaged ones from reuse. As with any history a seller asks you to take on trust, the paperwork proves what was done and the seller’s word proves nothing.

Then have the car inspected independently. On a Cat S car, that should include a wheel alignment and geometry check and an assessment of the structural repair against the manufacturer’s method. Uneven panel gaps, overspray and irregular tyre wear are all reasons to look harder.

An MOT certificate is no evidence of a good repair. The test checks the faults that most often fail cars on the day, not whether a structure was restored to its original dimensions, and a poorly repaired car can pass.

When It Is a Good Buy, and When to Walk

A professionally repaired Cat N on a common car, with full documentation, a clear explanation of the damage, an insurer willing to cover it and a fair discount, can be a sound purchase. The marker reflects damage that was dealt with, and the price reflects the marker.

A Cat S car with no repair documentation is a different proposition. So is any car where the seller is vague about the history, where the story does not match the category, or where a clean log book sits alongside a history check showing a marker the seller never mentioned. Any of those is a reason to walk away.

On an electric or hybrid car, ask specifically about the high voltage battery. The code allows a Cat N electric car to have compromised high voltage systems, so a buyer needs to know whether the battery was assessed, repaired or replaced, and by whom. Without a clear answer, the most expensive component in the car is an unknown.

If Your Own Car Is Written Off

The other side of the subject is the owner who has just been told their car is a write-off. Three things decide what happens next: the settlement offer, whether to challenge it, and whether to buy the car back.

The Settlement and How to Challenge It

The insurer pays the car’s current market value: what an equivalent car would have cost immediately before the loss, less any policy excess. The offer is a starting point, not a final figure.

An owner who thinks the offer is low can dispute it with evidence. Adverts for the same model at a similar age, mileage, specification and condition carry the most weight, along with service records and details of any factory options or recent work that raise the value.

If the insurer will not move, the next step is its formal complaints process. After that, the Financial Ombudsman Service handles disputes between consumers and insurers. A disagreement over the category itself follows the code’s own route, which escalates the question to an Appropriately Qualified Person, who makes the final decision.

Buying Your Own Car Back

An owner can buy back a Cat S or Cat N car, but not a Cat A or Cat B. In practice the insurer pays out the settlement less the car’s salvage value, and the owner keeps the car and the job of repairing it.

The paperwork follows the rules above. Keeping a Cat S car means sending the complete log book to the insurer and applying for a duplicate, which will record the category. Keeping a Cat N car means the existing log book can stay with the owner.

Either way, the marker attaches to the car from that point on. It will appear on every history check run against it, and it will take money off the price whenever the car is sold.

Buying back makes the most sense for an owner who knows exactly what was damaged, trusts a repairer to put it right, and plans to keep the car for years. On that basis the resale penalty counts for far less than the value of a car whose history the owner knows completely.

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