The MOT Loophole That Lets Garages Add £950 to Your Repair Bill

A faulty oxygen sensor that a fair-priced garage would fix for around £110 was quoted at £672 by a national chain in Leeds. That was the top figure from an undercover mystery shop that sent the same car, with the same known fault, to ten UK garages. Four of the ten also recommended extra work the car did not need, adding as much as £950 to the bill.

What the mystery shop found

Vehicle diagnostics company Carly ran the investigation using a Seat Ibiza fitted with a known, verified oxygen sensor fault. The same car went to independent garages and main dealers across England, and each was simply asked to diagnose and fix the problem, with no mention of the fault the investigators already knew was there.

Every garage correctly found the fault, so misdiagnosis was not the issue. Pricing was. The Leeds chain’s £672 quote for replacing both sensors sat at one extreme, while main dealers in Stoke-on-Trent and Sunderland quoted £618 and £328 for the same repair. A repair specialists say should reasonably cost around £110 in parts and labour ended up priced anywhere from three to six times that amount, depending purely on which garage the car happened to visit.

Four of the ten garages went further than pricing the known fault. They recommended brake replacements, spark plugs, air conditioning servicing or duplicate diagnostic checks unrelated to the sensor fault the car actually had. Carly’s investigators found these add-ons ranged from £400 to £950, on top of the sensor repair itself, and none were needed to fix the fault the car came in for.

A supporting survey of 2,000 UK motorists, carried out by OnePoll alongside the mystery shop, found widespread uncertainty about what a fair repair price actually looks like. Most drivers admitted they had no reliable way to judge whether a garage quote was reasonable, and relied largely on trust in the garage itself rather than any independent price comparison. That gap between what garages charge and what customers can verify is exactly the space in which overcharging and unnecessary upselling take hold.

The advisory system some garages use against you

The extra work garages pushed onto the Seat Ibiza mirrors a wider pattern in how MOT advisories get used. From May 2018 onward, every MOT result has come with one of four defect gradings: dangerous, major, minor or advisory. A dangerous or major defect fails the test outright. A minor defect still passes but should be fixed soon. An advisory flags something not yet bad enough to fail, but heading that way.

That advisory category is where the trouble tends to start. A tester can legitimately flag a tyre nearing the legal tread limit, or a brake pad with life left but wearing thin, as an advisory. Nothing about that requires immediate repair. Some garages present the advisory back to the customer as work that must be booked in straight away, without explaining that a minor or advisory grading gives the driver time to shop around, get a second quote, or simply keep an eye on the part until it needs attention.

Garages offering unusually cheap MOT tests, sometimes priced at £25 to £35 when the maximum fee for a class 4 vehicle is £54.85, have a financial incentive to make up that gap through repair work. That does not mean every cheap MOT hides an upsell, but it does mean drivers using a low-cost tester have more reason to check any advisory or recommended repair against a second opinion before paying for it. The maximum fee is a ceiling, not a fixed price, and many testers charge less, so a low quote on its own tells you very little about how the rest of the visit will be priced.

Who benefits from an unclear repair bill

Garages that upsell benefit twice over: once from the original repair, and again from add-on work the customer did not ask for and often cannot independently verify. Most drivers have no way to check whether a quoted price for parts and labour is reasonable, and few have the technical knowledge to challenge a garage’s judgement that a part “needs” replacing rather than simply being worth watching.

Not every garage behaves this way, and the trade has pushed back on blanket “rip-off” coverage, arguing that fair comparisons need to account for labour rates, diagnostic time and regional cost differences rather than treating every price gap as evidence of dishonesty. Even accounting for that, a six-fold difference in price for identical, verified work on the same car is difficult to explain through labour rates alone.

Main dealers are not automatically the safer option, either. The £618 quote from a main dealer in Stoke-on-Trent still sat well above the fair-price benchmark of around £110, even though it came from a branded, manufacturer-approved site rather than an independent garage. Brand reputation and dealer status did not reliably predict a fair price anywhere in the sample.

How to fight back against inflated repair quotes

Start with your car’s own MOT record. Every test result recorded from 2005 onward is free to view at gov.uk/check-mot-history using just the registration number, and it shows the exact grading, dangerous, major, minor or advisory, given to every defect at every test. If a garage tells you a repair is urgent, check whether the fault was actually recorded as an advisory rather than a major or dangerous defect. An advisory means you have time to make your own decision, not that the work must be booked immediately.

Ask the garage to write down the specific fault, the grading it was given and the parts involved before you agree to anything. A garage confident in its diagnosis should have no problem putting this in writing. If a quote feels high, take that written description to a second garage for a comparison price. Independent garages registered with a recognised trade body, such as the Independent Garage Association’s Trust My Garage scheme, commit to a code of practice that includes transparent pricing and a formal complaints process if something goes wrong.

For any repair over a few hundred pounds, get a second quote before agreeing. Garages know that customers rarely do this, and displaying a willingness to walk away and compare prices elsewhere is one of the simplest ways to avoid paying an inflated price. If a garage recommends work unrelated to the reason you brought the car in, ask directly why it is needed now rather than at the next service, and do not feel pressured to agree on the spot.

If you believe you have been overcharged or sold unnecessary work, you can raise a complaint through The Motor Ombudsman if the garage is accredited to one of its codes of practice, or through Trading Standards if you suspect the garage misrepresented the condition of your vehicle. Keep every invoice, the original MOT certificate and any written quotes, as these form the evidence needed to challenge a bill after the fact.

Before you hand your car over for its next MOT, spend ten minutes checking its existing advisory history on gov.uk so you already know what to expect. If a tester at the same garage suddenly flags something new and urgent that was not mentioned as an advisory the year before, that jump is worth questioning directly. Ask what changed, and ask to see the worn part itself where possible, rather than accepting a verbal description over the phone. A garage with nothing to hide will generally be happy to show you.

Sources:

• AM Online: Drivers overcharged by up to five times as repair costs surge, Carly finds
• Business Motoring: Undercover investigation alleges unfair pricing from garages
• GOV.UK: Check the MOT history of a vehicle