Thick fog across much of Britain has caused travel disruption with 10 percent of flights cancelled from London Heathrow, Europe's busiest airport.
The Met Office said the fog could reduce visibility to less than 100 metres but forecast it would lift by the afternoon.
A driver died and a five-year-old girl was injured on Sunday when a car apparently hit a tree in thick fog in Uttoxeter, central England.
Heathrow said about 45 flights had been cancelled, while London City, Manchester, Leeds Bradford, Glasgow, Belfast and Cardiff airports all reported delays.
"We've got extra passenger ambassadors in the terminals to provide assistance for those travelling today," said a Heathrow spokeswoman.
"Once again we would like to apologise for the disruption."
Heathrow officials met airlines and air navigation firm NATS to draw up a new schedule, and to decide which flights to cancel, said an airport spokeswoman.
In foggy conditions, airports have to switch to radar and "low visibility procedures" to ensure aircraft can taxi, take-off and land safely.
This increases spacing between aircraft by up to 50 percent as they have to taxi far enough away from the runway so that their instruments do not interfere with other planes.
Budget airline Easyjet warned it was suffering "major network disruption today due to poor weather conditions throughout Europe causing low visibility".
"This has resulted in a large number of aircraft and crew out of place for flights today," it said in a statement.
Britain has been enjoying an unusually mild autumn, with temperatures hitting 22C on Sunday, a November record.