What the Fog Light Rule Actually Means (and the £50 Fine)

• The Highway Code (Rule 236) says you must not use front or rear fog lights unless visibility is seriously reduced, and you must switch them off as soon as it improves. Seriously reduced generally means you cannot see for more than 100 metres (328 feet).
• Using fog lights in clear conditions can bring a fixed penalty notice of £50 (about $66), according to the AA, and the lights cause glare for other drivers and can hide your brake lights.
• A working rear fog light is also an MOT requirement: if the mandatory rear fog lamp does not light, it is a major defect and a fail.

When You Are Allowed to Use Fog Lights

Fog lights are allowed only when visibility is seriously reduced, which the Highway Code treats as generally meaning you cannot see for more than 100 metres. Rule 226 says you must use headlights in those conditions and that you are also allowed to use front or rear fog lights, but you must switch them off when visibility improves.

Rule 236 states the same rule from the other side, in capital letters: “You MUST NOT use front or rear fog lights unless visibility is seriously reduced”. Rule 236 gives the reason too: fog lights cause glare for other road users and can obscure your brake lights. So the rule is a ban with one exception, not a free choice.

The AA’s guidance matches this. It says fog lights are optional in genuine fog, headlights are required when you cannot see more than 100 metres ahead, and fog lights should never replace headlights. It adds that a blown headlamp bulb should be replaced quickly, and that insurers can dispute a claim if you crash in poor visibility without your lights on.

A quick way to judge 100 metres is to look for something you can identify at that distance, such as a lamp post, a road sign or a parked car. If you can still see it clearly, you do not need fog lights. If you cannot make out the vehicle in front until it is close, you do.

Why Using Them in Rain Can Cost You £50

The most common misuse is leaving the rear fog light on in ordinary rain or in the dark. The AA says using fog lights when visibility is clear can result in a fixed penalty notice with a £50 fine. At the 12 October 2026 rate of $1.3242 to the pound, that is about $66.

The reason for the rule is safety. The AA says leaving it on when it is not needed can cause glare for the driver behind or make them think you are braking. Rule 236 says fog lights can obscure your brake lights, which is the exact moment the driver behind needs to see them.

Heavy rain alone is not fog. Heavy spray can cut visibility sharply, but the Highway Code test is the distance you can see. If you truly cannot see more than about 100 metres, the lights are allowed, but you should switch them off the moment the spray clears. If the road ahead is visible, they should be off.

How Fog Lights Work and Which Cars Have Them

Every car has to have a rear fog light by law, but front fog lights are optional. The AA says rear fog lights are mandatory and front fog lights are not compulsory. Blackcircles, which covers MOT rules, says cars first used on or after 1 April 1980 must have at least one rear fog lamp, fitted on the centre or driver’s side.

Most cars have a single rear fog light, placed on the driver’s side or in the middle. Some have two. The AA warns that the second lamp can be mistaken for a brake light, which is another reason to switch them off once the fog clears. Fog lights are normally switched on by hand, so if they are on, you put them on.

Automatic headlights can mislead drivers in fog. The AA warns that automatic lights can fail to switch on in bright fog, so turn the headlights on manually if you need them. Daytime running lights are not the answer either, as they only light the front of the car, so nobody behind you can see you in fog.

The lights are only part of driving in fog. The AA says to slow down so you can stop within the distance you can see clearly, leave a three second gap to the car ahead rather than two, and do not follow another car’s tail lights, which gives a false sense of security. Rule 234 of the Highway Code says to check your mirrors and slow down before entering fog. Open the window at junctions to listen for traffic if you cannot see.

Fog Lights and Your MOT

Fog lights are part of the MOT, so a bulb that has failed can fail the car whether or not you ever use it. Blackcircles, whose article was last updated on 17 April 2026, says that if the mandatory rear fog light does not illuminate, it is a major defect and an automatic fail. If a car has two rear fog lamps, a failed nearside unit does not necessarily fail the test, but the driver’s side one must work.

The rear fog light also needs a working dashboard warning light, according to the same source. If the warning light does not come on, or the switch does not operate the lamp, that is a major fault. A loose lamp housing and a faulty switch are also major faults, and lens damage that changes the colour or visibility of the beam can be a major defect too. Rear lights must show steady red.

Front fog lights are treated differently. They are not legally required, and Blackcircles says they are only inspected on vehicles first registered on or after 1 March 2018 where they are fitted. For those cars, a front fog light that does not work is a major defect, and so is a multi source unit, such as an LED array, where more than half has failed. Older cars with front fog lights are not tested on them.

That means the cheap fix is to check the rear fog light before the test. Switch on the ignition and the headlights, press the fog light switch, and walk round the car or ask someone to look. A bulb is a small cost compared with a retest, and an MOT failure on a rear fog bulb is among the easiest to prevent.

Common Mistakes and Edge Cases

Three mistakes cover most misuse. The first is leaving the rear fog light on after the fog clears, which is the one the £50 notice is aimed at. The second is using fog lights in rain, where headlights and wipers do the job. The third is switching on fog lights at night on a clear road as a style choice.

There is a genuine edge case in the Highway Code wording. Rule 226 allows front or rear fog lights in seriously reduced visibility, and Rule 236 forbids them otherwise. The test is the visibility, not the weather label: the Highway Code does not name fog, rain or snow, it says seriously reduced, which it generally puts at 100 metres or less.

Another edge case is the dashboard warning light. Check the fog light symbol each time you set off and each time visibility improves.

If you are unsure, the safe default is simple. Use dipped headlights, slow down and keep your distance. Add the rear fog light only when the car behind you would struggle to see you, and switch it off once the road clears. That keeps you within the Highway Code, avoids the £50 notice and keeps glare off other drivers.

Sources

• The Highway Code: Driving in adverse weather conditions, Rules 226 to 237 (GOV.UK)
• The AA: Driving in fog
• Gazette: Highway Code, UK drivers £50 fog light fine warning
• Blackcircles: How faulty fog lights can fail your MOT test
• 30rates: GBP to USD rate, 12 October 2026