You have been driving in thick fog which has now cleared. You must switch OFF your rear fog lights because

Explanation: It is essential that the traffic behind is given a clear warning when you brake. In good visibility, your rear fog lights can make it hard for others to see your brake lights. Make sure you switch off your fog lights when the visibility improves.

Category: Vehicle Handling

References: The Official DVSA Guide to Driving: Section 12, Highway Code: Rule 114, Highway Code: Rule 226