Thousands of airline passengers have suffered fresh flight disruption as freezing fog hit the UK just days before the Christmas getaway.
A severe weather warning was issued by the Met Office covering southern and central England and some eastern parts of Wales until noon on Tuesday.
British Airways cancelled at least 49 departing and 49 arriving flights at Heathrow.
A number of flights at Gatwick, Stansted and London City airports were also cancelled or delayed due to the severe weather.
Passengers due to fly to or from European destinations on Tuesday were able to change their travel plans and re-book on to alternative flights up until Friday.
British Airways said it was reducing its short-haul flight schedules on Tuesday to “keep our customers safe in these challenging conditions”.
Heathrow said a “small number of flights” were cancelled in advance due to poor visibility at the west London hub.
A spokeswoman said this decision was made in partnership with air traffic control provider Nats “as a last resort to ensure safety”.
She added: “Regrettably, this may result in some passengers experiencing disruption to their journeys today and we advise they check flight status with airlines before travelling to the airport.
“As always, Heathrow’s top priority is the safety of our passengers and we apologise to those whose travel may be impacted by the weather.”
No flights were able to take off or land at Manchester Airport for several hours on Monday as one runway was shut due to fog and another was closed for emergency maintenance.
This led to the cancellation or delay of dozens of flights.
A Met Office yellow weather warning for fog was issued from 8pm on Monday to midday on Tuesday.
A spokesman said: “Fog is expected to form widely across southern and central England and some eastern parts of Wales on Monday evening, persisting overnight into Tuesday.
“Slower journey times are likely with delays possible to bus and train services. Some delays or cancellations to flights are also possible.”
It added that with light winds and clear skies expected to form quite widely on Monday night, visibility could fall below 100m (328ft) in some places.
Only a slow improvement in conditions is expected on Tuesday morning.
The yellow weather warning was issued for the East Midlands, the East of England, London and the South East, North West England, South West England, Wales and the West Midlands.
A British Airways spokesman said: “Freezing fog is expected across parts of Southern England and Northern Europe from early on Tuesday, December 19, and this is likely to affect flights arriving into and departing from London airports.
“In order to keep our customers safe in these challenging conditions, we have agreed to slightly reduce our short-haul schedules.
“We are doing all we can to contact customers whose flights are affected. If you are due to fly to or from European destinations on Tuesday, you may choose to change your travel plans and rebook onto alternative flights up until Friday 22 December.”
The airline added: “We are very sorry for the disruption to our customers’ journeys at this important time of year.
“We recommend that all customers check their flight is operating before travelling to the airport.”
This story was originally published in telegraph