Thousands of passengers are facing disruption as fog is forcing the cancellation of flights in and out of London.
Heathrow Airport and London City Airport in the Docklands have been affected throughout the day.
Heathrow said 132 flights, including 50 BA flights, have been cancelled due to heavy fog.
London City Airport suspended up to 44 flights and delayed or diverted others due to “low visibility” this afternoon.
The foggy conditions are expected to continue overnight, lifting around 10:00 GMT, the BBC weather centre says.
Severe fog warning.
A statement from Heathrow Airport, which deals with an average of 1,300 flights a day, said: “We are aware of 74 departing flights that have been cancelled by airlines. Some delays to flights are also occurring so we advise passengers to check with their airlines before travelling.”
A total of 58 incoming flights were cancelled.
Heathrow warned disruptions could continue late into the night.
Some airlines were re-booking passengers on other flights, while others were arranging for accommodation.
Some domestic passengers are being taken to their destinations by coaches, the airport said.
Heathrow Airport is open, but air traffic controllers have slowed the rate at which aircraft can land.
BBC Weather forecaster Holly Green said: “The fog was widespread across many parts of England on Sunday. Most areas saw the fog clear but Heathrow was one of the unlucky spots where it was thick enough to persist for much of the day.”
Matt Rigby, from London, spent the day at Heathrow having seen his midday flight to Moscow delayed and then cancelled.
He said: “Staff did not know what to do and gave conflicting advice.
“There were lots of other people standing around in queues back in the terminal in the same situation. It was all pretty chaotic.”
Mr Rigby said: “We weren’t even told it was due to fog, but I was able to figure it our for myself because it was pretty foggy out there.”
A Gatwick Airport spokesman said they had low visibility and had a couple of delays, but on the whole it was business as usual.
The Met Office has also issued a severe weather warning for areas of “dense fog” which were likely to become “more extensive” during the evening and night and could last until Monday morning.
Driving conditions could be “difficult” and motorists have been advised to take extra care.
BBC forecaster Ms Green said: “The fog cleared for a time in the evening as cloud moved over the airport but it may well return by Monday morning.
“The Met Office are warning the fog may cause further travel problems, particularly during Monday morning rush hour.”
A weather warning for dense fog also has been issued for Yorkshire and Humberside, the East and West Midlands, the East of England and the South East.
Fog has also affected large parts of Germany, the Netherlands and Belgium.