Car law checks for everyday driving

In Great Britain, five checks decide whether an ordinary car is legal to use today: window tint, tyre tread, headlights, fog lights and the number plates. GOV.UK's vehicle safety page, checked in 2026, says you are responsible for making sure the vehicle is always safe to drive, and that it can be unsafe even with a current MOT certificate. The numbers on the five topic pages come from that guidance, from the Highway Code, from the Construction and Use Regulations 1986 and from the Road Vehicles Lighting Regulations 1989.

Modern front windscreens must transmit at least 75 per cent of light. Modern front side windows must transmit at least 70 per cent. Cars, light vans up to 3.5 tonnes and light trailers, all first used from 3 January 1933, need at least 1.6 mm of tread across the central three quarters and around the full circumference. Headlights are required at night and when visibility is seriously reduced. Fog lights are only for that same seriously reduced visibility and must be switched off when conditions improve. Number plate characters must remain correctly spaced, clearly visible and legible.

No. GOV.UK says a vehicle can be unsafe even with a current MOT certificate. The tester records what was on the car on the day of the test. A bulb can fail the next week, a tyre can wear through the 1.6 mm line, and an aftermarket tint can be added after a pass. None of those wait for the next anniversary. Section 40A of the Road Traffic Act 1988 makes it an offence to use a vehicle in a dangerous condition, and that offence does not pause because a certificate is still in date.

The MOT is still the right place to find defects you cannot see from the driver's seat: headlamp aim, hidden cord in a tyre wall, a registration plate lamp that only works in the bay. Treat a pass as a snapshot. Treat the walk-round before you drive as the live check. GOV.UK tells you to check windows, mirrors, lights and brakes every time, then to follow the handbook for oil, coolant, brake fluid, the battery, washer bottles and tyres.

GOV.UK says you can be fined up to £2,500, banned from driving and given 3 penalty points for driving a vehicle in a dangerous condition. That is the headline figure for a car that is a danger, not a separate tariff for every bulb. Defective tyres have their own published figures: National Highways states a fine of up to £2,500 and 3 penalty points per illegal tyre, and DVLA records that as endorsement code CU30.

For window tint, GOV.UK says the police or a DVSA examiner can issue a prohibition notice that stops you using the vehicle until the extra tint is removed, and can follow that with a penalty notice or a court summons. Lighting offences sit under the Road Vehicles Lighting Regulations 1989. Incorrectly displayed number plates are a GOV.UK display offence and an MOT fail. A prohibition is immediate: the car stays off the road until the defect is put right, even if you intended to 'get it done next week'.

Start with what you can see and what you can switch on. Walk round with the ignition on, sidelights on, then headlights, then indicators, then fog lights, then the brakes with someone standing behind. Look at the rear registration plate lamp, because that lamp is a separate legal duty between sunset and sunrise. Look at both number plates for dirt, snow, missing characters and closing-up of the gaps.

Then look at the tyres on the ground. The legal reading is the lowest point in the central three quarters, all the way round, not the best groove on the outer shoulder. If you have a tread depth gauge, use the tyre tool on this site. If you have a light meter reading for the glass, use the tint tool. Neither tool replaces a look for cuts, bulges, cracks in the screen or a film so dark you cannot see a child at the kerb.

Tint, tread, fog lights and number plate display follow the same Great Britain regulations in Scotland as in England. Wales uses those same vehicle rules. The lighting rules do pick up one Welsh difference: Highway Code rule 113 says headlights at night are not required on a road with lit street lighting, and those roads are generally restricted to 30 mph, or 20 mph in Wales, unless signs say otherwise. That is a lighting exception tied to the restricted road definition, not a different bulb standard.

Northern Ireland is a different legal system for these checks. nidirect publishes the NI Highway Code text, and the DVA runs the NI MOT. Many of the same ideas apply, such as keeping lights working and tyres legal, but a GB figure on these pages is a GB figure. If you are preparing a car for an NI roadside check or an NI test, confirm the nidirect position rather than assuming the GB percentage, depth or lighting clock is copied across unchanged.

Nothing about the MOT anniversary pauses the offence. Using the car with an illegal tyre, with glass that fails the transmitted light test, or with lights that do not meet the Lighting Regulations is an offence on the journey you take today. If you cause a collision, the condition of the vehicle will be part of the investigation. A current MOT will not cancel that, and an advisory from last year's test that you never read is not a defence.

Insurance can also take an interest. A claim after a crash on illegal tyres or with no headlights in fog is the point at which a 'I was going to sort it' story gets expensive. The cheaper order of operations is: stop using the car, fix the defect, then drive. If a prohibition notice has already been issued, that order is compulsory.

The first is treating the MOT as a warrant that lasts a year. The second is measuring tyre tread on the outer shoulder, where the 1.6 mm test does not run, and concluding the tyre is fine while the centre is bald. The third is fitting a 70 per cent film to a modern windscreen and assuming that matches the 75 per cent legal test. The fourth is leaving rear fog lights on after the fog has lifted. The fifth is closing up plate characters to make a word.

Hire cars, company cars and courtesy cars produce a sixth mistake: assuming the owner is the one who will get the points. The driver is still the person using the vehicle. Check it before you set off, including the spare, the plates and the lights, even if you only have the keys for a day.

If you have a measurement, use the tools. Window tint and tyre tread are the two checks with a published number you can test at home. Lighting and number plates are rules you apply with your eyes and the switches. Read those pages after you have used the tools, not instead of them.

If you have no measurement and two minutes, do the walk-round in the order above: lights, plates, glass, tyres, brakes. That is the same list GOV.UK puts on the vehicle safety page, and it is the list that produces most roadside penalties and most MOT fails in this group of rules.

Window tint is a transmitted light test that changes with the first use date. Tyre tread is 1.6 mm in the central three quarters for post-1933 cars, light vans and light trailers, with a published £2,500 and 3 points per illegal tyre. Headlights are a night and poor-visibility duty under the Lighting Regulations. Fog lights share the 100 metre visibility test and must go off when the view opens. Number plates must show the issued mark correctly, and GOV.UK states both a fine and an MOT fail for getting that wrong.

Read the page for the check you actually have in front of you. The tint and tread pages have tools. The lighting and plate pages do not, because those rules are applied with switches and eyes, not with a percentage. All five sit under this hub so a driver doing a walk-round can move through them in order without hunting the rest of the site.