Rules for driving in adverse weather conditions, including wet weather, icy and snowy weather, windy weather, fog and hot weather.
Overview (rule 226)
Rule 226
You MUST use headlights when visibility is seriously reduced, generally when you cannot see for more than 100 metres (328 feet). You may also use front or rear fog lights but you MUST switch them off when visibility improves (see Rule 236).
LAWS: RVLR regs 25, RVLR regs 27