[mattn]

Checking the WoF VIRM it looks like they do not need to work. The heavy vehicle VIRM takes you to the same page.

"When switched on, a front fog lamp does not operate (Note 5)."

10. When switched on, a front fog lamp emits light that:.....

11. When switched on, a rear fog lamp emits light that is:
a) not projected to the rear, or
b) not diffuse, or
c) not substantially red, or
d) not approximately equal in colour or intensity from the other lamp in a pair, or
e) of variable intensity, or
f) not bright enough to indicate the presence of the vehicle from the rear in conditions of severely reduced visibility, eg due to modification, deterioration or an incorrect light source, or
g) altered, eg due to damage or modification.

Note 5
A forward-facing permitted lamp that does not comply with the equipment, condition and performance requirements must be made to comply, be removed from the vehicle, or be disabled so that it does not emit a light.

[mattn]

Interesing reading the VIRM's - I also always beleived "if its fitted, it has to work", however, that is not a reason for rejection. In fact, the VIRM's for lights general have a note along the lines of this one for high level stop lamps.

Mandatory lamp – the vehicle must have one high-mounted stop lamp that meets the equipment, condition and performance requirements. Any other high-mounted stop lamp is a permitted lamp. The permitted lamp is not required to operate, but if it does operate, it must meet the equipment, condition and performance requirements, although it may be obscured.

[96coaster]

When having a COF check, I asked the inspector whether he wanted me to engage reverse so he could check reverse lights and his reply was that they were not part of the checks and was not bothered.

[petercw]

My wof for the car guy would not issue me the wof until I either made my front spots work or removed them as he says any lights in place on the car had to work..I removed them.
At the cof. They test everything.. even rejected a working but broken reflector.

[mattn]

That's what they all say, many have said it to me, but that is not what the VIRM says. (Front Fogs have to work according to the VIRM, so your guty was right to make you fix or remove them.)

I have often wondered, based on the "If its fitted it must work", I get WoFs for my Caravan with a rear fog and reversing lamp not fitted, now I know - the VIRM says it does not have to work. However, mandatory lights have to work and have to be installed, and fog lights are about the only ones that are not mandatory and installed by manufacturers

[Nut17]

As the original question on this thread was for REAR fog lights which are a reasonably new phenomenon - A bit like having your stop lights permanently on, there is probably less likelihood they would be mandatory. The four Jeep Grand Cherokee's I have had since 2005 have them and certainly makes your vehicle lot more visible to following vehicles in foggy or misty rain conditions.

[Andycap]

Had rear fog lights back in the UK 40 + yrs ago . Mind you the fog there could be appalling ,mile after mile at 10kmhr . Only allowed to use in fog ,not misty rain, as the reflection off the wet road would allmost blind the person behind .

[NeilV]

Had rear fog lights back in the UK 40 + yrs ago . Mind you the fog there could be appalling ,mile after mile at 10kmhr . Only allowed to use in fog ,not misty rain, as the reflection off the wet road would allmost blind the person behind .

And that’s my pet gripe about ‘fog lights’ in general... many people use them like headlights, mostly REGARDLESS of whether there is fog or not