Flights from three London airports were hit by delays after fog shrouded the capital overnight, Britain's largest airline has said.
Festive travel plans faced being thrown into chaos after Heathrow, Gatwick and London City Airport all experienced a raft of hold-ups due to the weather.
The disruption came as Britain braced itself for the arrival of Storm Barbara, which is set to batter the country with strong winds.
Scotland is predicted to be the worst hit by the weather, with gusts of up to 90mph forecast in places.
Councils were said to be "fully prepared" for the onset of harsh conditions over Christmas.
The Local Government Association (LGA), which represents hundreds of councils in England and Wales, said it was issuing renewed advice on how to deal with flash floods and has stockpiled more than one million tonnes of salt to grit roads.
Environment spokesman Martin Tett said: "Councils are fully prepared to protect residents and minimise disruption caused by Storm Barbara and other potential bad weather such as snow and flooding. Council staff will be out in force clearing roads of any debris and damage."
It comes after a Gatwick spokeswoman said "about five or six" flights were diverted to other airports on Wednesday night due to fog and maintenance work on a runway, a spokeswoman said.
She added that normal service had resumed by Thursday morning, and they were taking flights diverted from London City.
Meanwhile, a Heathrow spokesman said some early-morning flights had been pushed back and there could be knock-on delays throughout the day, but added that there have yet to be any cancellations.
British Airways said on its official Twitter feed that it was aware of fog affecting flights at all three London airports and advised passengers to check their flight status online.
One flight due to arrive at Gatwick at 11.20pm on Wednesday was diverted to Birmingham Airport because of the fog, with passengers not making it to the London airport until shortly before 5am.
Mark Culverhouse, 46, who was on board, said: "The captain announced over the speaker that main runway was shut for construction and the support runway was not suitable because of the weather.
"The captain then said they were going to refuel and retry for Gatwick as the weather had eased, so we sat on the plane for a bit, then he announced they could not get fuel so we would have to leave the plane and transportation to Gatwick would be arranged.
"We were a bit annoyed as we should have been home around 1am. We are feeling very tired for work today."
The worst of any destruction from Storm Barbara is expected between Friday evening and Christmas Eve morning, but the potential for structural damage and disruption to some transport services means the storm's impact could be felt long after the winds have subsided.
Pockets of Northern Ireland, North Wales and the North of England are also due to feel the force of Barbara, which is due to roll in to the UK by Friday.
The UK Coastguard issued its own safety warnings ahead of the weekend.
Coastal operations area commander Ross Greenhill said: "We always advise people to check the weather and tidal conditions before they set out so that they can either prepare accordingly or consider whether they should even be going out at all."
Anyone who has problems with their power supply can call 105, a new, free national phone line available to people in England, Scotland and Wales.
The line was created by the Energy Networks Association after research suggested many people do not know who to contact if they have a power cut.
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