A seagull flies past the Big Ben clock on a foggy day in central London, November 2, 2015. [Photo/Agencies]

About 45 flights from Heathrow Airport, 10 percent of departures, have been canceled this morning. And a "considerable number" of flights have also been canceled because of poor visibility at London City Airport.

It said flights have also been affected at Birminghan Airport, Manchester Airport and Liverpool John Lennon Airport.

Drivers have also been advised to drive carefully due to heavy fog. Highways England said on its website that "Road users will need plenty of extra time to do their usual commute, especially as the fog is expected to lift very slowly during the morning."