Hundreds of flights have been cancelled and delayed across UK airports this morning due to heavy fog.
Heathrow has cancelled around 50 flights this morning and warned of further delays to other flights.
A spokeswoman for the 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."
Manchester, Leeds Bradford, Belfast and Cardiff are among the other airports reporting disruption.
The Met Office has issued a yellow weather warning across the UK due to poor visibility.
Passengers are being advised to check the status of their flight with the airline before travelling to the airport.