Originally Posted by Iain Mac

The Highway Code (Rule 94) says you must not drive with any foglights on except in conditions of seriously reduced visibility. That is defined in Rule 201 as "generally when you cannot see for more than 100 metres (328 feet)".

Apart from that, inappropriate use of foglights can be annoying to other road users and always gives me a laugh at the people who think having foglights is somehow either cool or effective.