A "fail" or "major" defect means the car is not roadworthy and cannot be driven (other than to a garage for repair). A "dangerous" defect means do not drive at all. An "advisory" is a warning of wear that will likely cause a fail within the next 12 months — your car still passes but you should plan repairs.
MOT terminology changed in 2018 and many drivers still find it confusing.
Pass + advisory
Car passes, certificate issued. Advisories are noted (e.g. brake pads getting low, slight oil leak). You can drive normally — but advisories often become fails next year.
Minor defect
Car still passes but the defect is recorded. E.g. small bulb out, slight wiper smear. Fix at convenience.
Major defect = fail
Car fails. Can only be driven to a garage to repair, or to a pre-booked retest at another MOT station. Driving otherwise = no MOT = invalid insurance + 6 points + £1,000 fine.
Dangerous defect = stop driving
Most serious. Car cannot be driven on the road at all. Recover to garage.
Retest
If repaired at the same garage within 10 working days, partial retest is usually free. After that, a full new MOT is required.
Can I drive home after an MOT fail? — Only if your old MOT is still valid. Otherwise, only directly to a repair garage or pre-booked retest.
Are advisories worth fixing immediately? — Tyres and brake pads usually yes — they get worse fast. Slight oil leaks or perished bushes can usually wait until the service.
More detail on: What's the difference between an MOT fail and an advisory?
The short answer above covers the usual case. Below is the extra detail a UK driver normally needs to act on it — how to narrow the fault down, what it should cost, and when it is worth paying a garage rather than carrying on. This is general guidance from a working mechanic, not a substitute for someone putting your own car on a ramp.
How the MOT actually works
The MOT is a snapshot of roadworthiness on the day, not a service and not a guarantee for the next twelve months. Defects are recorded as dangerous, major or minor, and advisories are the tester telling you something will need attention before long. You can present the car up to a month minus a day before expiry and keep the original renewal date. If it fails, you cannot drive it away except to a pre-booked repair or retest appointment.
Cheap things that fail MOTs
Every year the same avoidable items fail cars: blown bulbs, a torn wiper blade, washer fluid empty, a screen chip in the driver's swept area, tyres under 1.6mm across the central three-quarters, and a number plate that has been messed with. Ten minutes in the driveway the night before genuinely saves a retest. Registered brake imbalance, corroded brake pipes and worn suspension bushes are the ones that need a ramp.
When it is worth going to a main dealer
Three situations justify main-dealer money: an open safety recall (free), a live manufacturer warranty or goodwill claim, and coding or programming work that needs manufacturer-level software. Everything else — servicing, brakes, suspension, clutches, cambelts, diagnostics — an experienced independent will do to the same standard for a good deal less, and using an independent does not invalidate your warranty under UK block exemption rules as long as the correct parts and schedule are used.
Safe to keep driving?
Treat anything affecting brakes, steering, tyres, seat belts or visibility as stop-now, no matter how well the car appears to be driving. Overheating and low oil pressure are also stop-now: the damage curve on both is measured in minutes, not miles. Most other faults will let you drive gently to a garage, but if the car is in limp mode, losing fluid, or the fault changes how it steers or stops, get it recovered instead. Recovery is cheaper than a tow plus a new engine.
What Bob would check first
Start with the cheap, common and visible: fluid levels and their condition, tyre pressures and wear pattern, battery voltage and terminal condition, and every connector and vacuum pipe in the area of the fault. A surprising share of electrical gremlins are a corroded earth or a chafed loom, and a surprising share of running faults are an air leak downstream of the sensor doing the complaining. Only after that does anything get unbolted.
Get an answer on your own car
If you want this looked at properly for your exact vehicle, send the details and Bob will write back — make, model, engine, mileage, when the fault happens and any codes you have. You get a written reply from a qualified UK mechanic with 32 years on the tools, not a chatbot, and your money back if he cannot help.
Ask a mechanic about your car · Free MOT history check · Free recall check · Fault code library