Freezing fog causes hundreds of flights to be cancelled
Freezing fog is causing travel chaos across southern England, with thousands of passengers facings delays and cancellations.
Hundreds of flights have been cancelled at Heathrow and there have also been dozens of cancellations at London City Airport.
Gatwick has called off one flight and said there could be more delays.
Passengers are being advised to check flight statuses before leaving home.
The Met Office issued a severe weather warning for London, south-east England and parts of the south west over the fog - expected to remain in place until at least 10.30am.
Met Office forecaster Mark Wilson said Heathrow, Gatwick, London City and Stansted Airports all currently had very dense fog with just 100 metres' visibility.
A message on the Heathrow website said: "Foggy weather across London is expected on Monday 23 January and some passengers may experience disruption to their journey as a result.
"Heathrow advises passengers to check their flight status with their airline before coming to the airport."
Around 100 out of 1,300 departing flights were cancelled and a number of others were delayed as reduced visibility affected the tight take-off and landing schedule at Heathrow.
Thirty-three out of 132 departures at London City Airport were cancelled due to foggy conditions.
Gatwick Airport had nine cancelled departures, while Southampton Airport reported seven.
A Stansted Airport spokeswoman said there had not been any cancellations at the Essex airport, but advised passengers to check with their airlines for the latest information and allow enough time to get to the airport.
Road users were also warned of difficult driving conditions and icy roads.