Airlines have cancelled flights this afternoon and early evening after warnings of wintry weather for the UK.
British Airways said it has liaised with Heathrow Airport and air traffic officials and has agreed, along with other airlines, to reduce schedules.
It said flights at London Gatwick and London City could also be affected.
"The number of aircraft permitted to land by NATS at the Heathrow Airport from 15:00 GMT on Thursday is likely to be significantly reduced as the airport’s ground teams may need to remove snow and ice from the airport’s two runways and multiple taxiways," it said.
"Many aircraft will also have to receive de-icing treatment prior to departure to ensure that they are safe to take off. The safety of our customers and crews is our top priority at all times."
Heathrow Airport advised passengers to check their flight status and allow more time to get to the airport.
EasyJet told passengers it was still planning to operate its flying programme on Thursday as schedule but added: "We are closely monitoring the weather for any changes to the forecast."
Snow and sleet is forecast for many parts of Britain today with a risk of ice.
The Met Office is warning of ‘blizzard-like conditions’ in some parts of the country.
It said a cold and windy Polar maritime airmass will bring ‘a real taste of winter’ to the whole of the UK from today.
National severe weather warnings have been issued for wind and snow, with the heaviest and most frequent snow showers likely across northern and western Scotland, Northern Ireland and around Irish Sea coasts.
But it said eastern coasts will also be affected at times on Friday and Saturday.
"There will be gales which could lead to temporary blizzard conditions as well as a risk of hail and thunder in some locations," it added.
"Although the south of the UK is likely to avoid the majority of the snow showers, this area will have a wet day on Thursday with persistent heavy rain for much of the day, which is expected to turn to sleet or snow for a time in the afternoon and evening."
The Met Office said the cold weather will continue into Friday although snow showers will become more isolated.
