Travel conditions on the roads are expected to improve on Christmas Eve after thick fog in parts of England disrupted the holiday getaway for many.
Thousands of people are getting away for Christmas
The conditions forced nearly 140 flights from London airports to be cancelled on Sunday, while fog caused major disruption on several motorways.
Airlines said customers had been offered alternative flights or refunds.
Forecasters expect the fog to clear giving way to milder, wetter weather - with rain likely across the UK.
Fog affected parts of the M1, M4, M5, M6, M25 and M40 motorways. The BBC Weather Centre said visibility had dropped to 50m (164ft) in places.
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Of 86 flights cancelled at Heathrow, most were short-haul flights from Terminal 1, Terminal 2 or Terminal 4. Destinations include Edinburgh, Dublin, Milan and Rome.
At Gatwick, 21 cancelled flights included those with British Airways and Easyjet. The flights were bound for Amsterdam, Manchester, Newquay and Jersey.
A backlog of luggage belonging to people on cancelled flights built up
A spokeswoman at City Airport said 30 departures by Swissair, British Airways and Air France had been cancelled due to the fog, as well as a similar number of arrivals.
She said passengers due to take flights on Monday should check with their airlines in the morning.
Passenger Stephanie Adam had to scrap plans to see her parents in Basel, north-west Switzerland, for Christmas.
"I had my flight booked on the Friday night and it's been cancelled from City Airport... because of the fog. And then they rescheduled my flight on Sunday, today, and it's been cancelled again because of the fog."
Dozens of inbound journeys to the UK were also affected by the weather, with some flights cancelled and others diverted to alternative airports.
On an average day, a total of 1,250 flights arrive and depart from Heathrow.
A spokesman said that 181,000 passengers were expected in Heathrow's terminals on Sunday, slightly fewer than Saturday when 214,000 passed through.
Martin Vennard flew into Heathrow on Sunday evening and told the BBC News website he saw piles of luggage waiting to be collected by passengers whose flights were cancelled.
British Airways said all its customers facing cancellations would be refunded or offered the chance to re-book their flight on other available services.
A spokesman for Easyjet said the company had also only cancelled flights where there had been alternative options for passengers.
"Because the fog caused just a reduction in capacity, we had reasonable amount of flexibility to choose which flights to cancel," he said.
"Those passengers have been re-booked on flights going today and tomorrow. No-one is going to be left behind."
Sam Cooper, in London, told the BBC she was waiting for her partner to arrive from Edinburgh after his flight to Gatwick was cancelled and then rescheduled to Stansted.
"Fog is something we cannot control, let's be grateful for the staff helping everybody at this very busy time," she said.
Virgin Rail said there was still room on the company's pre-Christmas services for stranded air travellers.
A company spokesman added: "Our trains are running normally and there are still seats available. We'll do everything we can to help."
Stansted and Southampton airports - hit by fog in previous days - both said they were operating a normal service.
On the roads, fog delayed traffic on the M6 and the M40 motorways.
Trafficmaster said the east Midlands, the north of England and Scotland were particularly badly affected.
Problems were also reported on the M1, M4, M62, M60, M25 and the M5.
A 16-vehicle pile-up on the M5 near Bristol also caused delays. The crash at 5.30pm involved 15 cars and a coach and closed the motorway between junctions 17 and 18 for an hour.
A woman was airlifted to hospital with spinal injuries.
Earlier, motorists travelling from Sussex into Surrey on the northbound stretch of the M23 faced disruption following two accidents - one south of Gatwick Airport and another south of the junction for the M25, near Redhill.
Meanwhile in Northamptonshire, two crashes - one on the A14 at the junction with the M1 and another at the A421 at Evenley near Brackley - also caused long delays.
The busiest days on the roads after Friday's mass getaway are expected to be 27 and 28 December.
Rail travellers could yet face problems over the festive period because the West Coast Mainline is partially closing at Rugby for five days from 27 December.
Passengers are being advised to take alternative routes, such as the National Express East Coast, the Transpennine Express or Chiltern Trains into London Marylebone.