Nationally the picture barely moves from one year to the next, and it matches what we find on cars locally. Lighting, suspension, brakes, tyres and driver visibility between them cover most of what fails. Nothing exotic, nothing to do with engines or electronics — just the parts that wear, corrode or get forgotten.

Worth saying at the outset: a pre-MOT check is not about beating the test. It is about finding the cheap items before the test finds them, so you are not paying for a retest and a rushed repair at short notice.

1. Lighting And Signalling

The most common failure category, and the one with the cheapest items in it. A blown bulb fails the test. So does a lamp that is insecure, one of the wrong colour, one with a cracked lens letting water in, or a headlamp aimed badly enough to dazzle.

The bulbs people forget are the ones they cannot see from the driver’s seat: the number plate lamp, the rear fog light, the reversing light, and one of a pair of brake lights — because you do not notice a brake light out when the other one is working. Indicators are usually spotted, rear lamps often are not.

Headlamp aim fails a lot of cars, and owners are almost always surprised by it. Aim shifts when bulbs or units are replaced, after any front-end knock, and as suspension settles with age.

How to pre-empt it: get someone to work every switch while you walk round the car. Bulbs are a few pounds. Aim needs setting against a proper beam board, which is a short job. If your lenses are hazed, that is worth sorting at the same time — there is more on that in our piece on vehicle lighting.

2. Suspension

The second big category, and the least visible from outside the car. What fails here is mostly wear and corrosion: worn or leaking shock absorbers, split or perished bushes, worn ball joints, damaged or corroded springs, and corrosion of the mountings and subframe members that suspension components bolt to.

Broken coil springs are very common on British roads, particularly on cars that spend winters on salted routes and take a hammering from potholes. Quite often the driver has no idea — a snapped spring does not always change how the car feels much, and it is only found when the wheel comes off.

The corrosion angle deserves attention up here. Anywhere that gets gritted early and heavily, suspension mounting points and subframes corrode from below, and corrosion in a prescribed area near a mounting is a straightforward failure rather than an advisory.

How to pre-empt it: this one genuinely needs the car raised and someone looking. Bounce tests and eyeballing the tyres will not find a perished bush or a cracked spring. If the car has started knocking over bumps, feeling vague in corners, or crashing over potholes more than it used to, that is worth investigating before the test rather than after.

3. Brakes

Brakes fail for wear, imbalance and corrosion. Pads or shoes worn below the limit, discs worn thin or badly scored, brake pipes and hoses corroded or perished, a handbrake that will not hold to the required standard, an imbalance between sides on the rolling road, or fluid contaminated with moisture.

Brake pipes are the item worth singling out. They run the length of the car underneath, they are steel, and they corrode from the outside in where nobody looks. A badly corroded pipe is both an MOT failure and a genuine safety problem, because when a pipe lets go you lose part of the braking system with no warning at all.

Handbrakes fail more often than people expect, usually because a cable has seized or stretched on a car that spends most of its life on the flat and never has its handbrake worked hard.

How to pre-empt it: have pad and disc wear measured rather than guessed, get the brake fluid tested for moisture content, and have a proper look at the pipes underneath. Any judder, pull to one side or soft pedal wants sorting first — there is more detail in our piece on what brake noises mean.

4. Tyres

Tyres fail on tread depth below the legal minimum, uneven wear across the tread, damage — cuts, bulges, sidewall splits, exposed cords — incorrect or mismatched sizes on an axle, and on the spare or space saver where one is fitted and presented.

The detail that catches people is where the tread is measured. It is the central three quarters of the tread width across the whole circumference, so a tyre with plenty of tread in the middle and nothing left on one shoulder fails. That pattern is usually telling you something else as well — worn on the inside edge normally means alignment or a worn suspension component, worn in the centre or on both edges usually means pressures have been wrong for a long time.

How to pre-empt it: check all four across the full width, not just the middle, and check the inner shoulders, which means turning the wheels to full lock to see them properly. Look for bulges and cuts in the sidewalls while you are down there. If one tyre is wearing unevenly, fixing the cause is worth more than fitting a new tyre to wear out the same way.

5. Driver Visibility

The quiet category, and almost entirely made up of items costing very little. Wiper blades that do not clear the screen properly, washers that do not work or do not aim at the glass, an empty washer bottle on the day, damage to the windscreen in the driver’s critical vision area, and mirrors that are missing, broken or insecure.

Screen chips are the one that becomes expensive when ignored. A small chip in the driver’s line of sight can fail, and a chip left alone spreads — heat, cold and vibration all encourage it, and a frosty morning with the heater on full is exactly how a chip becomes a crack. Dealt with early it is often repairable; left to spread it is a new windscreen.

How to pre-empt it: replace blades that judder, smear or leave lines, fill the washer bottle with proper screenwash, check both jets actually hit the glass, and get chips seen to while they are still chips.

The Point Behind All Of This

Look at that list and the pattern is obvious: bulbs, blades, tyres, pads, a spring, a bush. These are not catastrophic components. The reason MOT failures feel expensive is timing — they get discovered at the worst possible moment, all at once, with a deadline attached.

A check a couple of weeks before the test turns that into an ordinary bit of maintenance you can plan around. We can do MOT preparation at your home or workplace, go through all of it properly, and tell you plainly what would fail, what would be an advisory and what is genuinely fine. MOT requirements do get updated from time to time, so check the current rules if you want the fine detail on any particular item.