What is freezing fog? London Heathrow cancels flights amid cold snap

London’s Heathrow Airport has cancelled flights as freezing fog gripped the city amid a wider cold snap battering the country.

About 30 flights, or 5 per cent of Heathrow’s departures, were grounded by slippery and icy conditions on the runways, with British Airways being the most affected, tracking website FlightAware said.

Heathrow Airport recorded its coldest night since December 2010 and coldest January night since 1987 as temperatures dropped to minus 8.4°C.

Freezing fog happens when the temperature falls to below zero and can be particular dangerous for drivers.

Airlines were on Monday trying to rebook passengers on alternative services later in the day, with the fog expected to begin clearing at 10am.

“Like other airlines, our schedule has been affected by the continued freezing fog weather experienced across London,” a British Airways spokesman said.

“We've apologised to customers whose flights have been affected and are doing everything we can to get them on their way as quickly as possible.

“We advise customers to check the website for the latest flight information.”

The cancelled flights included planes for Amsterdam, Barcelona and Miami.

“Poor visibility is forecast this morning at the airport and across the South-East,” a Heathrow spokesman added.

“While there may be minor changes to today's schedule as a result of the weather, we want to reassure passengers that our colleagues are working in close collaboration with our airline and air traffic control partners to get them safely away on their journeys as quickly as possible.

“We encourage passengers to check with their airline for the latest information.”

The Met Office tweeted: “What a contrast this morning. Stepping out of the door across the North-West of the UK and you can ditch the gloves … though ice scrapers at the ready in the South-East.”

Temperatures are not expected to rise above zero in London until midday and are unlikely to top 4°C, while they could reach 10°C by mid-afternoon in Northern Ireland.

Sunday saw mixed weather across the UK as milder air moved into northern and western parts, while southern and eastern areas remained cold.

Network Rail said passengers were delayed at London Charing Cross because ice on the conductor rail meant trains could not draw power, but they are now working normally.

London Fire Brigade told people to be careful when using an open fire to stay warm.