https://youngcardriver.com/driving/driving-in-fog

Driving in fog

When driving in fog you should slow down, use low beam headlights, and leave plenty of distance ahead in case a sudden stop is needed.

For severe weather warnings

Before you travel in severe weather conditions, keep up to date with the latest about what to expect.

Met Office – for all weather warnings.
Environment Agency – for all flood related warnings

Fog affects driver perception

Fog can drastically reduce your visibility to other road users. Of course, theirs to you – you can be driving in good conditions and then suddenly encounter fog – you simply might not see it coming.

Be careful: even when the fog seems to be clearing up you can find yourself back in the thick of it in a matter of seconds.

The best advice if you are driving in fog

The Highway Code states that when driving in fog you MUST use your headlights if your visibility is reduced to 100m or less. Also use your fog lights, but remember to switch these off as soon as visibility improves.

Following a car’s rear lights can be comforting but can also give you false sense of security. Make sure you keep a safe distance between you and the car in front.
When slowing down be aware it may only be your brake lights that are warning drivers behind you that you are slowing down. They may not be able to see anything else, so use your brakes with that in mind.
Drive at a speed that allows you to pull up within the distance you can see clearly, particularly on motorways and duel carriageways as you will be travelling faster.
Be aware of other drivers not using headlights.
At junctions only emerge when you are sure it is safe to do so. If necessary, wind down your window and listen out to confirm the way is clear and don’t hesitate once you are in a position that is directly in the path of oncoming traffic.
Don’t forget to use your windscreen wipers and the demister.