As a rough rule, if the repair costs more than half the car's value, or the failures are structural corrosion, think hard. Brakes, tyres, suspension and lights are almost always worth fixing.
Every spring Bob has the same conversation with owners of ten-year-old cars: is it throwing good money after bad? The answer is more often yes than people expect.
Start with the actual numbers
Get the full failure list from the VT30 certificate, then a written quote for the work. Look up what your car actually sells for — not what you hope, but what similar mileage and condition examples are advertised at, minus a bit. Then ask what replacing it would cost: a newer car brings purchase price, higher insurance, higher road tax in many cases, and the unknown faults of somebody else''s car. A £700 repair bill on a £2,000 car that you know the history of is frequently the cheaper year of motoring than buying a £4,500 replacement.
Failures that are almost always worth fixing
Brake pads, discs, hoses and handbrake adjustment. Tyres. Bulbs, headlight aim and number plate lights. Wipers and washers. Suspension bushes, drop links, anti-roll bar links, track rod ends and ball joints. Exhaust blows and broken mounts. Emissions failures caused by a lambda sensor, air filter or EGR valve. These are all wear items with predictable, capped costs, they use standard parts, and fixing them puts the car back into a known-good state. None of them says anything bad about the car''s future.
Failures that should make you stop and think
Structural corrosion within 30cm of a suspension or seatbelt mounting point is the big one — welding a sill or a chassis leg properly is £400 to £1,500 and, crucially, where you find one rotten area on a UK car there are usually three more starting. Failed catalytic converter combined with high mileage. A chronic emissions failure that diagnostics cannot pin down. Extensive subframe corrosion. Any failure where the estimate contains the words further investigation required and the car is already worth less than £1,500. These are the ones where the bill tends to grow after the car is on the ramp.
The hidden question: what is coming next?
Look at the advisories as well as the failures. Advisories are the tester telling you what will fail next year. A car that failed on two bulbs but has advisories for corroded brake pipes, a weeping shock and a cambelt overdue is not a £60 repair — it is a £900 repair spread over nine months. Ask the garage for an honest view of what else is close. A good independent will tell you straight if a car is at the end of its economic life, because they have no interest in doing £300 of work on something that will be scrapped in March.
Typical UK repair costs to weigh up
Front pads and discs: £180 to £320. Rear pads and discs: £160 to £300. Two tyres fitted: £110 to £280. Front suspension arm: £150 to £300. Drop links, pair: £90 to £160. Rear shock absorbers, pair: £220 to £420. Exhaust centre or rear section: £120 to £300. Lambda sensor: £90 to £220. Handbrake cables: £120 to £250. Brake pipe replacement, full set: £300 to £600. Welding per section: £150 to £400. Retest is free at the same garage if you leave the car and it is retested within ten working days, or by the end of the next working day if you take it away.
What you can and cannot do with a failed car
Once a car has failed and the old certificate has expired, you may only drive it to a pre-booked MOT test or to a garage for repairs. If it failed on a dangerous defect, you must not drive it at all until that defect is repaired — the police can and do act on the MOT database. You can still tax it only with a valid MOT, so a long repair gap means a SORN. Insurance also becomes questionable on a car with a dangerous-rated failure, which matters if the worst happens.
Bob''s rule of thumb
If the repair bill is under a third of the car''s value and the failures are wear items, fix it without hesitating. Between a third and a half, fix it if you know the car and its history and the advisories are clean. Over half the car''s value, or any structural corrosion, get a second opinion before committing — and make that second opinion a proper inspection, not another quote off the same failure sheet. Cars are scrapped every day that had two grand of life left, and cars are repaired every day that should have been let go.
Can I drive my car if it failed its MOT? — Only to a pre-booked test or to a garage for repairs, and only if the old certificate has expired. If it failed on a dangerous defect you must not drive it at all.
Is the MOT retest free? — Yes if you leave the car at the testing station and it is retested within ten working days, or if you take it away and return it before the end of the next working day. Otherwise a partial or full fee applies.
Can I take my car elsewhere for the repairs? — Absolutely, and you should get a second quote if the bill is significant. You are never obliged to have the testing station do the work.
Does a failed MOT go on the car''s record? — Yes. Failures and advisories are recorded on the DVSA database and are visible to anyone checking the car''s MOT history, including future buyers.