Is it illegal to drive with rear fog lights on?

Yes, when visibility is not seriously reduced. The Road Vehicles Lighting Regulations 1989 prohibit using rear fog lamps except in seriously reduced visibility, and the Highway Code repeats it as a MUST NOT, adding that you must switch them off when visibility improves. Police can and do issue a fixed penalty notice for it. The reason is not pedantry: a rear fog lamp is roughly as bright as a brake lamp and sits near it, so a following driver is both dazzled and less likely to notice you braking.

When should I use rear fog lights in the UK?

Only in seriously reduced visibility, which the Highway Code describes as generally being when you cannot see for more than 100 metres. That is fog, dense spray, heavy snow or torrential rain — not ordinary darkness, not drizzle and not dusk. The honest test is whether you can see the vehicle in front from a distance: if you can, the car behind can see you, and your fogs are doing nothing but harm. Switch them off as soon as the conditions lift, which on a British motorway can be within a mile.

Do rear fog lights fail an MOT?

They can, in two different ways. Vehicles first used on or after 1 April 1980 must have a rear fog lamp fitted to the centre or offside of the car, and under section 4.5 of the inspection manual an obligatory rear fog lamp that is missing, inoperative or the wrong colour is a major defect. Separately, the dashboard tell-tale for the rear fog lamp is inspected under section 4.9.1, and a tell-tale that is missing or does not work is also a major defect. A lens that is cracked or discoloured enough to affect the light emitted fails too.

What is the difference between the front and rear fog light symbols?

Colour, and which way the lines point. Both symbols show a lamp with a vertical wavy line cutting through the beams — the wavy line is the fog. The rear fog tell-tale is amber and its beam lines are horizontal, pointing right. The front fog tell-tale is green and its beam lines slope downwards, pointing left. The colour is the quicker tell: amber for rear, green for front. It matters because the rear lamp is the one that dazzles people and the one drivers most often leave on by mistake.

Dashboard warning light

Rear fog light warning light

Last updated 27 July 2026

Quick answer

The rear fog lamp is switched on. Nothing has broken — but unlike most amber lamps this one is asking you to do something, because using rear fogs when visibility is not seriously reduced is an offence. They are far brighter than a tail lamp, they dazzle the driver behind, and they sit close enough to the brake lamps to mask them.

What to do: No action needed
Can you drive?: Yes

Why it is amber

A system has reported a malfunction, or something needs attention. The car is usually still driveable, but the fault will not clear itself and several amber lamps are an automatic MOT failure.

What turns it on

Pressing the rear fog switch. On most cars the rear fog can only be switched on when dipped beam or the front fog lamps are already on, and the inspection manual allows rear fogs to extinguish when main beam is selected or when dipped beam is switched off. Some cars cancel the rear fog every time the ignition is switched off; plenty of others remember it, which is exactly how people end up driving around on a clear night with them on.

What to do about it

Switch them off the moment visibility improves. This is not advice, it is the law: the Highway Code says you must not use front or rear fog lights unless visibility is seriously reduced, and you must switch them off when it improves.
Use the amber tell-tale as your check. If it is lit and you can comfortably see well past the car in front, the fogs should be off.
Get into the habit of glancing at the dashboard when you set off, particularly the morning after a foggy drive home. A car that remembers the setting will happily light them again for you.
If you are being flashed by drivers behind and cannot work out why, this lamp is the first thing to check.
If the tell-tale does not light when you switch the rear fog on, book it in. The rear fog tell-tale is a testable item in its own right and a dead one is a major MOT defect.

Can you keep driving?

Yes

The car is fine and the lamp is working as designed. What is not fine is leaving it on in clear conditions, which is a lighting offence and can bring a fixed penalty notice. It also actively reduces safety for the driver behind you, who is being dazzled and may not pick out your brake lamps against the glare.

What causes it

The switch has been left on from a genuinely foggy journey
The switch has been knocked, which is easy on the many cars that put it in the same cluster as the headlamp switch
The car remembers the setting through an ignition cycle rather than resetting it
Front and rear fogs share a single switch on some cars, so selecting one selects both

Does it fail an MOT?

Not on its own — but what causes it often does.

Two separate MOT rules touch this lamp, and neither is recorded here to avoid double-counting. The tell-tale itself falls under the same mandatory tell-tale defect as main beam in section 4.9.1, where a missing or inoperative main beam or rear fog tell-tale is a major defect — see the main beam warning light page for the recorded failure figures. Separately, the rear fog lamp itself is tested under section 4.5: vehicles first used on or after 1 April 1980 must have one working rear fog lamp fitted to the centre or offside, and a missing obligatory rear fog lamp or one that does not work is a major defect in its own right.

Common questions

Is it illegal to drive with rear fog lights on?: Yes, when visibility is not seriously reduced. The Road Vehicles Lighting Regulations 1989 prohibit using rear fog lamps except in seriously reduced visibility, and the Highway Code repeats it as a MUST NOT, adding that you must switch them off when visibility improves. Police can and do issue a fixed penalty notice for it. The reason is not pedantry: a rear fog lamp is roughly as bright as a brake lamp and sits near it, so a following driver is both dazzled and less likely to notice you braking.
When should I use rear fog lights in the UK?: Only in seriously reduced visibility, which the Highway Code describes as generally being when you cannot see for more than 100 metres. That is fog, dense spray, heavy snow or torrential rain — not ordinary darkness, not drizzle and not dusk. The honest test is whether you can see the vehicle in front from a distance: if you can, the car behind can see you, and your fogs are doing nothing but harm. Switch them off as soon as the conditions lift, which on a British motorway can be within a mile.
Do rear fog lights fail an MOT?: They can, in two different ways. Vehicles first used on or after 1 April 1980 must have a rear fog lamp fitted to the centre or offside of the car, and under section 4.5 of the inspection manual an obligatory rear fog lamp that is missing, inoperative or the wrong colour is a major defect. Separately, the dashboard tell-tale for the rear fog lamp is inspected under section 4.9.1, and a tell-tale that is missing or does not work is also a major defect. A lens that is cracked or discoloured enough to affect the light emitted fails too.
What is the difference between the front and rear fog light symbols?: Colour, and which way the lines point. Both symbols show a lamp with a vertical wavy line cutting through the beams — the wavy line is the fog. The rear fog tell-tale is amber and its beam lines are horizontal, pointing right. The front fog tell-tale is green and its beam lines slope downwards, pointing left. The colour is the quicker tell: amber for rear, green for front. It matters because the rear lamp is the one that dazzles people and the one drivers most often leave on by mistake.

This is general guidance, not a diagnosis. Manufacturers draw the same system differently and reuse symbols for more than one function, so check the handbook for your own car before acting on anything here.

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