The “flow rate” of arrivals has been reduced for safety reasons.

More than 20 short-haul services to and from Heathrow have so far been cancelled. Most are with British Airways, which has the majority of operations at Britain’s busiest airport.

BA flights to and from Aberdeen, Amsterdam, Basel, Brussels, Edinburgh, Milan and Newcastle have been axed.

Aer Lingus flights to and from Belfast, Cork and Shannon have been cancelled, as well as a Lufthansa service to and from Frankfurt.

Poor visibility is also affecting services at Gatwick and London City — where six early morning arrivals have been diverted. Flights from Amsterdam, Antwerp, Dusseldorf, Zurich and two from Luxembourg landed instead at Southend or Stansted. Departures to Glasgow and the Isle of Man were cancelled.

British Airways tweeted: “Fog is affecting flights at London Heathrow, Gatwick & City today.”

With few spare seats on flights so close to Christmas, the number of cancellations is a concern. Around 3,000 passengers have so far been affected.

Passengers whose flights are cancelled because of poor weather do not automatically get re-booked on the next service to their destination; travellers booked on that flight take priority.