Thick fog has caused scores of flight cancellations with poor visibility lasting for most of the day in London and parts of south east England.
Worst hit was London City Airport in London's Docklands where the bad weather meant very few services were able to operate.
By mid-afternoon a total of 172 flights had been axed at Heathrow airport in west London where many other services were delayed.
"It's started off foggy, then it cleared for a time but then it came down again," said a Heathrow spokeswoman.
She added that Heathrow was advising passengers to check with their airline about flights.
At London City the arrival and departure boards were covered in cancellations, with those outside the city able to see for themselves the extent of the fog through pictures posted on Twitter.
One picture showed the scene looking out from the control tower at London City, with a controller staring into what appeared to be a white out.
Blanketing most of south east England, the fog also led to delays to Wightlink Ferries, which operates routes between Hampshire and the Isle of Wight.
Today's flight problems follow last Saturday's major disruption at all airports after difficulties at the Hampshire headquarters of air traffic control company Nats.
Then yesterday an accident involving a landing aircraft at Stansted meant no planes were able to land at the Essex airport for around three hours.