Hundreds of passengers could be stranded in hotels over Christmas because of flight cancellations and long delays at Heathrow caused by fog.
Up to 200 people could be stranded in hotels for Christmas because of flight cancellations and delays at Heathrow.
The airport cancelled 64 flights as a knock-on from Sunday's problems but said the situation would improve later because the fog had already lifted.
The airport has cancelled 64 flights because planes and crew were in the wrong airports after fog led to 86 flights being cancelled on Sunday.
All of the flights scheduled to leave before Christmas Day are now full.
Airport operator BAA said services should now be back to normal.
Gatwick has cancelled seven incoming and seven outgoing flights. London City has cancelled six outgoing flights.
But it said all scheduled Christmas flights were now fully booked and that meant many of those originally booked onto cancelled services were now stuck.
Passengers have been urged to check with their airport before travelling.
Overnight train
Stranded for Christmas
Greg Ward, operations director for BAA at Heathrow, said perhaps as many as 200 people would have to spend Christmas in hotels.
On Sunday, 140 Heathrow flights were cancelled, leaving more than 1,000 people stranded overnight.
He told BBC News: "BA's flights are at capacity now, so we're actually telling people to leave - we're giving them vouchers to stay in hotels - and to re-book online or over the phone."
A British Airways spokesman said: "Due to the way things have gone, there may be those who won't get to where they want.
He said: "People are obviously upset... but actually in fairness a lot of people understand it's not got anything to do with the airlines or the airport."
"We would expect to get as many people away as possible, but we can't rule out the possibility of some people not getting away. Our staff at the airport are working as hard as they can."
On the railways, more than 200 passengers are stranded on the overnight sleeper from Euston to Inverness at Carstairs near Glasgow, after the train hit what Network Rail described as "material" on the track.
On the railways, more than 200 passengers are stranded on the overnight sleeper from Euston to Inverness at Carstairs near Glasgow, after the train hit what Network Rail described as "material" on the track.
'Just unbelievable'
The flights cancelled from Heathrow on Monday were due to depart from terminals one and four to destinations including Newcastle, Dublin, Glasgow, Edinburgh, Aberdeen, Paris, Barcelona, Rome and New York.
The flights cancelled from Heathrow on Monday were due to depart from terminals one and four to destinations including Newcastle, Dublin, Glasgow, Edinburgh, Aberdeen, Paris, Barcelona, Rome and New York.
A British Airways spokesman said: "Due to the way things have gone, there may be those who won't get to where they want.
"We would expect to get as many people away as possible, but we can't rule out the possibility of some people not getting away. Our staff at the airport are working as hard as they can."
Thousands of people are getting away for Christmas
Thousands of people are getting away for Christmas
Greg Ward, operations director for airport operator BAA at Heathrow, said perhaps as many as 200 people would have to spend Christmas in hotels.
About 1,000 people had to spend the night at Heathrow following Sunday's cancellations.
He told BBC News: "BA's flights are at capacity now, so we're actually telling people to leave - we're giving them vouchers to stay in hotels - and to re-book online or over the phone."
Tibor Mezei, from Hungary, unhappy with Heathrow's planning.
He said: "People are obviously upset...but actually in fairness a lot of people understand it's not got anything to do with the airlines or the airport."
'Just unbelievable'
Stranded traveller Tibor Mezei, from Hungary, was unhappy with Heathrow's planning.
It is the second Christmas Eve in a row he has been stuck at Heathrow, on both occasions he has been on his way from Los Angeles to Budapest.
It is the second Christmas Eve in a row he has been stuck at Heathrow, on both occasions he has been on his way from Los Angeles to Budapest.
He told BBC News: "It's just unbelievable. No-one can give me instructions. I'm here with luggage and a two-year-old, and honestly there's been zero information."
He told BBC News: "It's just unbelievable. No-one can give me instructions. I'm here with luggage and a two-year-old, and honestly there's been zero information."
At London City Airport, the website listed one cancellation to Edinburgh, with the five others to European destinations.
At London City Airport, the website listed one cancellation to Edinburgh, with the five others to European destinations.
Gatwick Airport said six outgoing domestic and short-haul flights have been cancelled, in addition to six incoming flights.
Gatwick Airport said six outgoing domestic and short-haul flights have been cancelled, in addition to six incoming flights.
Stansted Airport reported being very busy, but with only minor delays.
Stansted Airport reported being very busy, but with only minor delays.
Airports across other parts of the UK were also largely keeping flights on schedule.
Airports across other parts of the UK were also largely keeping flights on schedule.
Milder weather
Milder weather
Manchester Airport said two BA flights were cancelled earlier due to the repercussions of cancellations around London.
Manchester Airport said two BA flights were cancelled earlier due to the repercussions of cancellations around London.
Four flights were also cancelled from Edinburgh Airport for the same reasons - two destined for Heathrow, one for London City Airport and one for Birmingham.
Four flights were also cancelled from Edinburgh Airport for the same reasons - two destined for Heathrow, one for London City Airport and one for Birmingham.
Glasgow Airport had one flight cancelled in the morning, also to Heathrow. There were no other delays at either airport, a spokeswoman said.
Glasgow Airport had one flight cancelled in the morning, also to Heathrow. There were no other delays at either airport, a spokeswoman said.
A BAA spokesman said the cancellations on Monday were the result of aircraft and crew being in the wrong places following the problems caused by the fog.
Forecasters expect milder, wetter weather over the coming days - with rain likely across the UK.
Forecasters expect milder, wetter weather over the coming days - with rain likely across the UK.
Have you been caught up in delays? Are you stuck at an airport? What are you planning to do as a result?
Have you been caught up in delays? Are you stuck at an airport? What are you planning to do as a result?
