Travel misery is likely to blight the UK until after Christmas, with the long-awaited thaw not expected until Boxing Day.
Forecasters predict sub-zero temperatures will persist over the coming days, hampering efforts to free up Britain's frozen transport network.
The travel plans for many thousands of people are already in ruins, with airport operator BAA warning that Heathrow faces more delays and cancellations until potentially beyond Christmas Day. Meanwhile, Gatwick safely reopened its runway at 6am on Tuesday, but the airport said passengers should expect further disruption, with delays and cancellations inevitable.
There were also warnings of more long queues for Eurostar passengers at St Pancras station in London, after thousands were forced to wait for up to eight hours on Monday in bitterly cold weather.
On Monday night first-aiders from St John Ambulance were sent in as a precaution while people shivered in lines that stretched around the terminal building.
The coldest temperature in the UK overnight was in Crosby, Merseyside, which sunk to minus 17.6C (0.3F).
Shap in Cumbria recorded minus 15.4C (4F), along with Capel Curig in north Wales. It was similar temperature at Tyndrum in the Scottish Highlands. However, central London saw a much milder night, with the mercury hovering just above 0C (32F).
Transport Secretary Philip Hammond relaxed the rules on night flights on Monday in a bid to ease the passenger backlog at Heathrow. The Government has agreed to relax night flights, allowing for arrivals until 1am until Christmas. And flights into London will be allowed to operate 24 hours a day.
But despite the moves, the airport was likely to operate at a reduced capacity until Friday, Mr Hammond said. The UK's roads and rail network has also been badly hit.
Giving a statement to the Commons, Mr Hammond said disruption was "inevitable" given the severity of the weather conditions and that the transport system would "struggle to recover" in the days leading up to Christmas with more poor weather expected.