Christmas travellers have endured a third day of misery as thick fog caused flight cancellations and delays, but the weather should improve on Saturday.
Restrictions have been put on flights because of poor visibility
More than 300 flights were cancelled at Heathrow on Friday, including all British Airways domestic flights.
BA plans to start domestic flights to and from Heathrow from midday on Saturday, and hopes to operate 95% of its Heathrow services through the day.
Train firms provided extra services and the roads generally flowed on Friday.
BA hopes to operate 87% of short-haul flights on Saturday, and plans a full Heathrow service on Sunday, including resuming services to Paris and Brussels.
In all, 411 flights were cancelled at Heathrow and other airports on Friday.
About 40,000 people were affected, with many having to switch to roads and rail instead.
BA transported thousands of passengers to UK destinations from Heathrow by coach.
British Airways customers should contact 0800 727 800
or check the www.britishairways.com
website to see if their flight is still operating
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Network Rail said three million people travelled on nearly 20,000 trains - the entire national rolling stock.
The Highways Agency has suspended more than half of its 83 roadworks, and many rail engineering works are also being delayed until Christmas.
The flight cancellations came about after air traffic control placed restrictions on flights landing and taking off at Heathrow, because of the low visibility.
BAA, which runs several UK airports including Heathrow, laid on food and drink for passengers and facilities such as heated marquees, blankets, ponchos, towels and children's entertainment.
But some passengers complained about having to join the queues at Heathrow, and others were trying to sleep whilst sitting at tables.
"The fog is not in the sky so much as in the minds of the BA directors," said David Ranan, 60, whose flight from Heathrow to Munich was cancelled.
Geoff Want, BA's director of ground operations, apologised to customers and said the airline was "working around the clock" to try to get people to their destinations.
The airline says passengers whose flights have been cancelled are entitled to a full refund.
Other airports, including Norwich, Bristol, Cardiff and Southampton, were also disrupted by fog, and other regional airports suffered knock-on effects from Heathrow, with flights to Heathrow being cancelled.
Meanwhile forecasters at the BBC's Weather Centre said they were "reasonably confident" visibility would improve around Heathrow on Saturday, as the fog moved north.
Most of England and Wales has been affected, with only the north of England, the south coast and parts of Cornwall escaping the fog on Friday.
People who have opted to travel by car could also face jams on major routes as last-minute Christmas-shoppers and people travelling home for the festive break head for the roads.
The RAC said an estimated 18 million people were expected to be driving over the next few days.