Red-flag MOT advisories: when to walk away from a used car
6 min read · Updated 6 July 2026
Buying a used car in the UK? The MOT history on gov.uk tells you almost everything you need to know — if you understand what you''re reading.
Most listings look fine at first glance. It''s the pattern in the MOT history that gives the game away. Here are the advisories that should make you walk away, and the ones that are basically noise.
Walk away immediately: structural corrosion
If any MOT advisory or failure mentions the word "corrosion" near a structural area, stop reading and move on. This includes:
- Subframe corroded / corrosion within 30cm of a mounting point
- Sill corroded (structural)
- Chassis leg corroded
- Suspension mount corroded
- Rear subframe mounting prescribed area corroded
Structural corrosion is the single most expensive thing to fix on a used car. Welding a subframe or sill on a £3,000 hatchback costs £800–£2,500 and often uncovers more rust once the panels are opened up. On anything under £6,000 it''s an instant "no".
Cosmetic surface rust ("light corrosion", "corrosion beginning") on a non-structural panel is normal on any car older than 8 years. Don''t confuse the two.
Walk away: repeated emissions failures
An MOT emissions failure on a diesel usually means one of:
- Failing DPF (diesel particulate filter) — £800–£2,500 to replace
- Failing EGR valve — £400–£900
- Failing catalytic converter — £300–£1,500
One emissions failure that passed on retest can be fine (the garage cleaned it, drove it hot, or replaced a sensor). Two or more emissions failures across different MOTs means the underlying part is on borrowed time.
Serious concern: transmission and clutch mentions
MOT testers don''t formally test clutches, but they note things like "clutch slipping on road test" or "transmission noisy" in advisories. On a manual, a clutch is £600–£1,200 fitted. On a DSG or automatic, transmission work starts at £1,500 and often goes past £3,000.
If you see these mentions on a car under £5,000, factor the repair into your offer or walk.
Normal wear — not a dealbreaker
These come up on almost every used car and are fine to negotiate £50–£200 off for, but shouldn''t stop the deal:
- Tyre worn close to legal limit — £60–£120 per tyre
- Brake pads worn but within limits — £80–£200 per axle
- Wiper blade damaged — £15–£40
- Bulb not working — £5–£30
- Registration plate lamp inoperative — £10
- Minor oil leak — usually just a rocker cover gasket, £80–£250
- Play in a lower suspension arm — replace the arm, £150–£300
The pattern to actually look for
Open the last 4 MOTs on gov.uk. You''re looking for the same advisory repeating year after year without being fixed. That tells you the owner has been driving with a known problem, and it''s about to become your problem.
If a car has 40,000 miles between MOTs, that''s also a red flag on an older car — high mileage in a short time usually means motorway commuting, which is actually kinder to a car than short urban trips, but it also means big service items (cambelt, water pump, DSG oil) are due sooner than the odometer suggests.
Cross-check with Vehicle Scouter
Vehicle Scouter pulls every UK car''s MOT history and cross-references known common faults for that model. If a Peugeot 308 has a chocolate timing chain and the MOTs show a "slight rattle on cold start" advisory, we''ll flag it for you before you view the car — not after you''ve bought it.
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