Mechanic-maintained breakdown of MOT defect wording by inspection category, plus quotes journalists can cite and a press contact at a working DVSA-approved UK garage.
What the national MOT failure data shows
Across millions of UK tests each year the pattern barely changes: lighting and signalling is the biggest single failure category, then suspension, brakes, tyres, and driver's view of the road. Roughly a third of cars fail first time, and a large share of those fail on something the owner could have checked in the driveway.
That is the useful takeaway. Bulbs, wipers, washer fluid, tyre tread and a cracked windscreen in the swept area account for an enormous number of failures that cost almost nothing to prevent.
How failure rates change with age
A three-year-old car has a very low failure rate. By eight to ten years old, suspension components, brake corrosion and tyres start driving failures. Past twelve years, structural corrosion becomes the expensive category, especially on cars that live near the coast or on gritted Scottish roads.
Mileage matters less than you would expect. A low-mileage car that sits still corrodes its brake discs, perishes its tyres and seizes its callipers while a high-mileage motorway car sails through.
Using the data before your test
Work down the failure categories in order and check them yourself: every lamp including the number plate and reversing lights, wiper blades and washers, tyre tread across the full width, obvious play in the steering, and the windscreen in the swept area.
Then have a garage look at brakes and suspension, which you cannot properly assess from the ground. An MOT at Bob's is £54.85 and a pre-test check beforehand is cheaper than a retest and a wasted week.
Frequently asked questions
What percentage of cars fail the MOT?
Around a third of cars fail at first test, and a large proportion of those fail on easily preventable items.
What is the most common failure category?
Lighting and signalling, followed by suspension, brakes and tyres.
At what age do cars start failing more?
Failure rates climb sharply from around eight years old, driven by suspension, brake corrosion and tyres.
Do low-mileage cars pass more easily?
Not necessarily. Cars that sit still suffer corroded discs, seized callipers and perished tyres.