When can I use fog lights?

You may use front or rear fog lights when visibility is seriously reduced, generally when you cannot see for more than 100 metres. Highway Code rule 226, checked in 2026, states that test and cites the Road Vehicles Lighting Regulations 1989, regulations 25 and 27. You must use headlights in those conditions. Fog lights are extra, not instead. Rule 236 then says you must not use front or rear fog lights unless visibility is seriously reduced, and you must switch them off when visibility improves.

The 100 metre figure is the Highway Code's working definition of seriously reduced visibility. It is not a measured fog density on a dashboard. If you cannot see that far, headlights must be on and fog lights may be on. If you can see further than that, fog lights must be off. Ordinary rain, spray that has not closed the view down to 100 metres, and night on a clear road are not the test. They are the conditions in which rear fog lights dazzle and hide brake lights.

Yes. Rule 236 is a must-not rule. Front and rear fog lights must not be used unless visibility is seriously reduced, because they dazzle other road users and can obscure your brake lights. Switching them off when the fog lifts is the same legal duty as switching them on when you cannot see 100 metres. Leaving them on in a queue on a clear night is the version of the offence everyone behind you can name.

Rule 234 deals with the sign that causes the other mistake. If 'Fog' is shown on a sign but the road is clear, be prepared for a bank of fog or drifting patchy fog ahead. The sign is a warning, not a permission slip. Keep the fog lights off until the view actually closes down, then use them, then switch them off as soon as you can see again.

The DVSA car and passenger vehicle manual, section 4.5, inspects front fog lamps fitted to vehicles first used on or after 1 March 2018, and the one rear fog lamp that must be fitted to the centre or offside of vehicles first used on or after 1 April 1980. An obligatory rear fog lamp that is missing or inoperative is a major defect. The lamp must show a steady red light. Front fog lamps must show a steady white light. The switch must work from the driving seat.

Front fog lamps that are not wired up and have no corresponding switch are not required to work. If the tester is not sure they are connected, the manual says to give the benefit of the doubt. Rear fog lamps may be combined with the rear position lamps. A mandatory tell-tale for the rear fog lamp that is missing or inoperative is a major defect. Tricycles and quadricycles are outside this fog lamp MOT requirement.

Using fog lights when visibility is not seriously reduced is a Lighting Regulations offence under the same regulations rule 236 cites. GOV.UK does not publish a specific fixed penalty amount for this on the pages cited here, so this page does not invent one. Dazzling other road users is also forbidden by rule 114. A defective obligatory rear fog lamp is a construction and use and MOT issue as well as a lighting-use issue.

If the fog itself is the problem, the duty is to slow down. Rule 235 says keep a safe distance, be able to pull up well within the distance you can see, use wipers and demisters, and do not accelerate to get away from someone too close behind. Rear lights in fog give a false sense of security. Headlights stay on. Fog lights stay on only while the 100 metre test is met.

The 100 metre test does not change because the vehicle is a van, a hire car, a company car or a motorcycle. If the bike has fog lamps, the same use rule applies. Many motorcycles do not have them, which simply means the headlight duty in fog is doing all the work. A trailer must have working lights, and DVSA's towing safety guidance tells you to check them before you tow. A rear fog lamp on the trailer is part of being seen, not a reason to leave the car's rear fog lamp on in clear air.

Foreign cars in Great Britain are using GB roads. The GB Highway Code rule is the one a GB officer will apply. Disabled drivers and older drivers get no published relaxation of the 100 metre test. If anything, the duty to be seen and not to dazzle matters more when reaction times are longer.

Rules 226 and 236 apply in England, Scotland and Wales. The 100 metre test does not change at those borders. Wales changes the default restricted-road speed to 20 mph, which is a different page. Northern Ireland publishes its own Highway Code text on nidirect. Use that version for an NI roadside discussion, and treat the figures here as the GB rules.

The MOT dates above are GB MOT manual dates. Northern Ireland's DVA test has its own inspection manual. Do not assume a 1 April 1980 rear fog requirement is copied word for word into the NI scheme without checking.

Leaving rear fog lights on after the fog lifts, especially on a motorway at night, is the classic. Using them in rain because the road is wet. Using them because a sign said fog five miles ago. Using front fog lights as daytime running lights. Forgetting that headlights must be on as well. Assuming a working front fog lamp on a 2010 car is an MOT item: the front fog MOT check is for vehicles first used on or after 1 March 2018.

The other mistake is not using them when you truly cannot see 100 metres, so the car behind finds you the hard way. The rule is not 'never use fog lights'. It is 'use them only while the view is that short, and switch them off the moment it is not'. Snow, smoke from a moor fire, and spray behind a lorry on a wet motorway can all meet the 100 metre test. Each of those can also lift in a few seconds, which is why the off-switch is part of the duty.

Judge the view, not the weather app. If you cannot see 100 metres, headlights on, then fog lights if the car has them. Tell-tale on the dashboard should light for the rear fog lamp. Slow down so you can stop within the distance you can see, which is rule 235, and leave a bigger gap than feels natural because the car in front is only a pair of lights. When a clear patch opens, fog lights off, headlights as the night and visibility rules require.

Front fog lights help you see the painted edge and the verge. Rear fog lights help the driver behind see you. Using only the rears in thick fog, with no headlights, is the wrong way round. Using only the fronts on a clear night, as extra driving lamps, is the other wrong way round. The Lighting Regulations duty is the 100 metre test, applied continuously, not once per journey.

Slow down, and stop if you need to, which is the same advice rule 115 gives for dazzling headlights. Do not retaliate by switching your own rears on in clear air. That is the offence in the other direction. There is no published GOV.UK process for reporting a dazzle incident as a lighting offence, so this page does not invent a form number. If the dazzle is part of a collision, it is a fact for the report. If it is just unpleasant, drop back and wait for the lamp to go out.

In a stationary queue, take your foot off the brake once the car behind has stopped, so your stop lamps do not add to the glare. That is already in rule 114. Rear fog lamps left on in that queue are the worse version of the same glare, because they are designed to punch through fog.