Air passengers are facing another day of disruption as dozens of flights are cancelled from Heathrow due to thick fog.
About 45 flights - 10% of departures from Heathrow Airport - were "pre-cancelled" on Monday as most of England and east Wales were issued a weather warning for fog.
Passengers encountered long delays on Sunday at Britain's busiest airport.
Some planes had to be grounded on Sunday night due to the fog at Heathrow
Those hoping to take off on Monday may also be disappointed as Heathrow advises people to check with their airlines to see whether or not their flight is cancelled.
Gatwick and London City Airport were affected by the weather on Monday.
A spokeswoman for Heathrow Airport said: "We've got extra passenger ambassadors in the terminals to provide assistance for those travelling today.
"Once again we would like to apologise for the disruption."
Passengers are advised to check with their airline for updates.
Those hoping to travel through Gatwick have been advised to check ahead for any disruption.
Images shared on social media this morning show the poor weather conditions at Heathrow Airport.
The Met Office weather warning is valid until midday, with fog expected to slowly clear throughout the morning.
The forecaster said the fog would become widespread and dense overnight into today and warned: "Travel may be impacted by poor visibility, with some minor disruption expected."
Visibility could be reduced to less than 100 yards, it added.
On Sunday, Heathrow cancelled about 50 flights.