Fog was affecting flights from Heathrow and London City airport this morning with warnings of disruption and cancellations.
A total of 120 flights at Heathrow have been cancelled this morning, including more than 20 British Airways flights with the airline issuing a caution that fog in the London area may disrupt services early today.
London City airport said that flights were suffering from disruption due to low visibility this morning.
Passengers were advised to call their airlines for more information.
The bad weather came on top of a raft of flight cancellations to Spain due to a five-day strike by cabin and ground staff at BA sister carrier Iberia.
The Spanish airline is running a reduced schedule on most routes, with only services to the Balearic and Canary Islands operating as normal.
BA is operating a reduced schedule to Madrid, Barcelona and Malaga while flights to Alicante, Ibiza and Palma are expected to operate as normal.
One BA flight from Gatwick to Malaga is to operate with a two-hour onward coach transfer to Gibraltar provided.