Snow is expected to blanket the UK for the next week, with freezing temperatures causing hazardous conditions and further delays and cancellations after three days of transport disruption.
Heathrow, one of the world's busiest airports, said it would cancel about 130 flights on Monday after cancelling twice that number on Sunday.
After a £36m investment in cold weather equipment since 2010, when snow almost shut it down just before Christmas, Heathrow said it was coping with the wintry conditions. The reduction in capacity on Sunday was mainly owing to low visibility rather than snow on the runways, it said.
Passengers complained of long delays waiting on board aircraft for planes to be deiced. Airlines, which are responsible for deicing, said they were doing all they could to get planes off the ground.
British Airways said it had called up more than 100 volunteer personnel to help with deicing, which was taking more than 30 minutes per plane because of the freezing conditions and persistent snowfall.
Heathrow said it would normally have aircraft arriving or departing every 45 seconds. But low visibility meant that "at the moment that spacing is doubled and that's why we are running at a reduced capacity," a spokeswoman said.
On Sunday the airport said its snow-clearing operations were running according to plan. A spokeswoman said it was "a myth" that other airports had not experienced disruption because of the snow, pointing to problems at Munich, Geneva and Frankfurt, as well as 40% of flights being cancelled out of Paris.
The airport said that because it operates at almost capacity, there was "simply no room to reschedule … delayed flights".
Over the weekend, travellers at airports in Yorkshire and the Midlands were also frustrated by delays and disruption caused by the weather. After cancelling or diverting 20 flights on Friday night, East Midlands airport said only heavy and persistent snowfall would force further cancellations. London City airport also had to cancel 50 flights after remaining closed for most of Sunday.
There was good news for 2,000 residents in County Down after engineers worked through Friday and Saturday to restore power.
Gianfranco Zola, manager of Watford football club, paid tribute to more than 100 supporters for clearing their home pitch of snow on Saturday. The match against Huddersfield ended in a 4-0 victory for the home side.
The Met Office has issued yellow warnings for ice for much of the country and advised people to take extra care in the subzero conditions. Up to 20cm of snow is expected to fall on higher ground in Scotland and the Pennines on Monday, while strong winds are also forecast, with potential for drifting snow.
Southern trains, which includes services between London and Brighton, and Southwest trains put out amended timetables, including a number of cancellations, before rush hour. Parts of the Severn bridge look likely to remain closed on Monday
Edmund King, the head of the AA, said conditions for drivers could be like skating rinks. "Snow is still falling heavily in Hertfordshire, Kent, West Midlands and in a band across the south-east, spreading north and east," he said. "Main roads and motorways are coping quite well with the snow so far.
"However, many drivers can't get off their local residential streets and cul-de-sacs. The hidden danger is the sheet ice below the inch or two of fresh snow on ungritted local roads where snow and slush from yesterday has frozen."
Sally Webb, a forecaster with MeteoGroup, said: "We expect it to remain cold and there to be snow or sleet for the next week in most areas.
"It will also be icy everywhere, especially with the snow melt, and temperatures are going to be no more than 1C, dropping below zero overnight."