Further delays and cancellations are plaguing Britain's busiest airports.
Heavy snow and freezing conditions have seen flights grounded and many passengers sleeping on hard floors for another night.
People hoping for a Christmas getaway have found themselves stranded, with hundreds camping out in terminals overnight.
Temperatures have plunged overnight, with a record low for Northern Ireland seen in Castlederg, County Tyrone, where the mercury plunged to minus 17.6C. The lowest UK temperature overnight was thought to be minus 19.6C, recorded in Chesham, Buckinghamshire.
Forecasters have said the UK is experiencing some of the most severe winter weather in a century, with continued sub-zero temperatures and snowfalls of up to 20cm expected on Monday.
Motoring organisations have warned of "potentially fatal" conditions on the roads as commuters struggle into work, with others hoping to make an early start to their Christmas holidays.
Air and rail passengers are being urged to check before they travel while road users are being warned to travel only when necessary.
Mayor of London Boris Johnson has questioned BAA chief executive Colin Matthews over the situation at Heathrow, asking if everything possible had been done to get the airport moving.
He said: "I stressed the huge economic importance of Heathrow. If there was a war on we'd surely be able to sort this out."
The mayor has also been in talks with Transport for London (TfL) all weekend.
Shadow chancellor Alan Johnson has hit out at the Government's handling of the situation, saying people felt they had been told to "get a shovel or stay at home".
Transport Secretary Philip Hammond defended his approach, saying he had been consulting with the Government's chief scientific office about the need for major long-term investment.
Passengers were unforgiving, despite airports saying they were doing all they could.
Trevor Taylor, 37, waiting for a flight to Singapore with his wife and two young sons, described the scene at Heathrow's Terminal 5 as "absolute mayhem".
Mr Taylor said: "Frustration is building up. I've been sleeping on a knobbly marble floor and every space you can see is taken."
Singer Lily Allen was among those caught up in delays at Heathrow, writing on Twitter before her flight left: "Terminal 3 carnage. Apparently our flight is going today. Lots of tinfoil blankets all over the place. Departures is a ghost town."
Eurostar services have also been affected, with an emergency timetable in operation for the rest of the week. A Eurostar spokesman urged passengers not to travel unless it was absolutely necessary, with refunds or rescheduled tickets available to those who could postpone their journey. Speed restrictions on Eurostar services are also adding up to two hours to journey times.
Train operator East Coast has warned passengers there will be longer journey times and cancellations throughout the day. Yesterday all services were suspended between King's Cross, London, and Peterborough due to damage to overhead power lines.
Those hoping for a white Christmas may be disappointed however - one forecast for Christmas Day itself is labelling it "wet and windy".