Fog was affecting flights from Heathrow today for a second morning in succession.
Heathrow said: ”It remains foggy here so please check your flight status with your airline.”
London City airport advised passengers this morning to call their airlines for more information this morning due to disruption caused by low visibility.
Thick fog led to at least 300 flights being cancelled yesterday from Heathrow and London City.
At least 80 were cancelled at Heathrow due to poor visibility while some inbound services to London City were diverted to Stansted.
Southampton airport was also forced to cancel 16 flights yesterday morning due to the poor weather conditions.
More cancellations and delays were expected this morning at Heathrow due to the backlog from yesterday and the fog returning, mainly affecting short-haul European services.
Eurocontrol said this morning that fog was also affecting Gatwick, Oslo, Amsterdam, Hamburg and Munich with snow at Istanbul airport.
Heathrow said 40 flights have been cancelled this morning despite the fog beginning to lift.