More than 20 flights from Heathrow have been cancelled this morning due to freezing fog and ice.
Further cancellations and delays are expected at the London hub and others including London City Airport where at least 18 flights were dropped yesterday.
Flights affected from Heathrow include services to Warsaw, Nice, Stockholm, Aberdeen and several German cities.
A Heathrow spokesman told the BBC: “It’s better to cancel flights when there’s fog because you can’t land as many planes per hour because you have to leave more space between the planes.”
Cancelling in advance helped airlines accommodate passengers on other flights, he added.
The disruption came as the Met Office issued a yellow warning of fog for parts of England until 11am this morning.
Dense and freezing fog in London and across much of central, eastern and northwest England was forecast.
Other fog-affected airports this morning included Gatwick and Leeds/Bradford, although there is no reported disruption at Gatwick.