Before May 2018, a UK MOT had two outcomes: pass and fail. The defect that pulled your car up could be a failed number-plate bulb or a catastrophically cracked brake disc — the certificate treated them the same. The DVSA reformed that in 2018 and introduced a four-tier defect system that aligns with European standards. The system is more useful, but only if you know what the tiers actually force you to do.
How the four categories work
The four categories on a current MOT certificate are Dangerous, Major, Minor, and Advisory. The first two cause a fail. The second two don’t.
That’s the short version. The longer version matters, because the category attached to each defect has legal and insurance implications that go beyond whether the certificate says PASS or FAIL.
Dangerous — you don’t drive home
A Dangerous defect is a direct and immediate risk to road safety or to the environment. A tester can only apply this category when the defect is so severe that driving the vehicle away would create a real risk of harm.
Real examples from DVSA’s inspection manual:
- Brake disc worn or scored below manufacturer’s minimum — if a disc is so thin it risks fracturing under braking, that’s Dangerous. A disc that’s worn but still within tolerance is something else entirely.
- Windscreen cracked in the driver’s primary vision zone (the area swept by the wiper, in front of the steering wheel) — a crack that impairs vision or risks sudden failure under speed is Dangerous. A chip in the upper corner, away from the wiper arc, generally isn’t.
- Steering seriously defective — significant play in the column or a rack so worn that the vehicle can’t track straight is Dangerous. Mild play, worn but within limits, will land differently.
The legal position is unambiguous. A vehicle with a Dangerous defect cannot be driven on a public road. Not even to the garage around the corner. If you drive it, you are committing an offence under the Road Traffic Act — and more practically, you are almost certainly driving uninsured. Most motor policies contain a roadworthiness clause; a Dangerous-tagged vehicle clearly fails that test.
The only legitimate way to move a Dangerous vehicle is on a trailer or flatbed. If the test station is unable to arrange this and you have no other option, contact your insurer before moving the car.
Major — the car fails, but you’re not necessarily stranded
A Major defect is a significant defect — one that affects safety or emissions — but not one that presents an immediate risk. The car fails its MOT, but the tester has judged that the vehicle can be moved for the purpose of getting it repaired.
Real examples:
- Number-plate lamp not working — this one surprises people. A lamp that illuminates the rear registration plate is a legal requirement at night. If it’s out, that’s a Major. The fix is a £2 bulb, and most testers will give you a few minutes to sort it if you have a spare in the car, but if the circuit is blown rather than just the bulb, you’re looking at an electrician’s time.
- Stop lamp not functioning — a single brake light is Major. No brake lights at all tends to escalate toward Dangerous depending on the tester’s judgement and the condition of the reflectors.
- Tyre tread depth at or below 1.6mm — the legal minimum is 1.6mm across the central three-quarters of the tyre, all the way around. Below that is a Major. A tyre showing cord (the fabric layer beneath the rubber) is more likely to attract a Dangerous rating.
You can drive a Major-failed vehicle directly to a repair, but the honest answer is that you’re doing so at your own risk. Nothing in the legislation grants explicit permission; what exists is an accepted convention that enforcement won’t typically pursue a vehicle that is being driven specifically for repair, with a clear paper trail showing the failed MOT and a booking at a garage.
If the item costs more than the quote you receive on the day, the MOT cost estimator at /tools/mot-cost-estimator/ is a useful cross-check against the range of prices typically charged across UK centres for that specific repair category.
Minor — noted, but not a fail
A Minor defect doesn’t cause the test to fail. The car receives a pass certificate, but the defect is recorded on the VT20 with its RFR code so there’s a permanent record.
The purpose of the Minor category is to flag things that don’t currently break the standard but are heading that way. A tyre wearing unevenly but still above 1.6mm might be Minor. A wiper blade that leaves a narrow uncleared stripe but doesn’t impair vision might be Minor.
The practical consequence: your car is road-legal, your MOT is valid, but you’ve been formally told about a condition. That condition is logged in the national database against your registration. If the same item becomes worse and gets re-examined the following year as a Major, there’s now a documented history showing it was noted previously.
Minor items should be treated as a short-to-medium-term to-do list, not ignored. The inspection manual defines the boundary between Minor and Major fairly precisely, but wear progresses.
Advisory — information, not instruction
An Advisory is not a defect at all. It’s the tester passing on an observation that sits outside the pass/fail framework — something they noticed during the test that might be worth knowing about, even if it doesn’t meet the threshold for any of the defect categories.
Common advisories from the failures index at /failures/:
- “Nearside rear tyre wearing on inner edge — consider wheel alignment check”
- “Rear brake pads at approximately 2mm — approaching service limit”
- “Minor oil weep from rocker cover — monitor”
None of these fail the car. None of them are legally significant. An advisory is the tester doing you a favour by noting something they spotted. You can act on it or not.
What advisories are not: a list of upselling opportunities. Some centres use the advisory section heavily to generate workshop bookings. If you receive a VT20 covered in advisories, cross-reference them against the DVSA inspection manual or get a second opinion on the items that look expensive.
How testers decide between categories
The inspection manual sets out precise criteria for most items, but tester judgement does come into it at the margins. Two testers looking at the same vehicle might rate a windscreen chip differently, or a suspension bush at different severity levels depending on how they read the play.
There are things testers cannot do. They cannot charge for a retest of items they repaired themselves within the same session — the DVSA rules specifically prohibit charging a full retest fee for items fixed during the test window at that station. If your car failed on a bulb and you replaced it in the car park within the test window, the retest of that item should be free.
The key lever you have as a vehicle owner is the gov.uk check. Every defect, every category, every RFR code is logged. If a tester repeatedly assigns Dangerous to items that other centres rate as Major, that pattern appears in the data. It won’t help you on the day, but it does mean the system isn’t entirely opaque.
The category doesn’t change the cost to fix
This is worth saying plainly. A Dangerous defect doesn’t cost more to repair than a Major defect — the category describes the risk level at test, not the price of the part or the labour. A Dangerous stop-lamp circuit fault might cost £15 in parts and twenty minutes of labour. A Major windscreen crack might cost £400 to replace.
The category should influence how urgently you act — Dangerous means today, Major means before the car goes back on the road. It shouldn’t be the sole factor in how you budget for the repair.