Fresh snow has been falling across many parts of the UK, bringing disruption to some areas not previously affected.
Hundreds of schools closed, driving conditions have been hazardous, and rail and air passengers were delayed.
The Met Office has issued heavy snow warnings for Yorkshire and Humber, east Midlands, east and north-east England, London and south-east England.
It also warned of further heavy snow in parts of Scotland and widespread ice on roads across the whole of Britain.
In Scotland, heavy snow warnings have been issued for Grampian, Central, Tayside and Fife and south west Scotland, Lothian Borders.
BBC weather forecaster Nina Ridge said snow showers would persist into Tuesday night across north-east England and parts of north Midlands and Lincolnshire.
But a line of snow stretching across south-east England towards Dorset would drift southwards and ease, she added.
Temperatures are expected to tumble well below freezing into Wednesday, with the greatest risk of heavy snow in northern England.
The recent cold spell has hit schools, roads, and airports, and the worst-affected areas have been north-east Scotland and north-east England.
As the snow moved southwards in sub-zero temperatures, disruption was widespread. It included:
- Severe disruption for air passengers at Gatwick Airport where flights have been suspended. Edinburgh International is also suffering severe delays
- Less serious but widespread delays at other airports across the UK. Passengers are advised to check with their airline
- Two lanes closed on the M25 anticlockwise at A282, Dartford Tunnel
- Snow is also causing severe delays on the M25 between J29 and J3
- In Kent severe delays on A20 coastbound between Crittal's Corner, Sidcup and Swanley Interchange because of snow
- In North Yorkshire, the A169 is shut in the Whitby area because of drifting snow. One lane closed on A66 Scotch Corner, both ways between Scotch Corner and A685 junction in Brough, due to snow
- In Cumbria, the A592 Kirkstone Pass is closed between the Troutbeck junction and the Hartsop junction, because of snow. One lane remains closed on the A66 between A6108 and A685 junctions. The A686 Hartside Pass Langwathby is also closed
- West Yorkshire, A1 closed and queueing traffic northbound between the A639 Doncaster Road junction in Little Smeaton and the A1(M) J40 junction in Wentbridge, because of snow and a jackknifed lorry
- Number of roads are closed in Derbyshire because of ice and snow, including the A57 at Snake Pass
- Delays and cancellations on some train services from Kent into London, with East Coast rail services running an amended timetable. Services from London into Surrey also affected
- Passengers trying to travel from Newark to Lincoln face night sleeping on the station after all connecting road and rail services cancelled.
- Around 850 schools were closed in Scotland, with at least six councils planning to close schools for a third day
- Hundreds more were closd in England, including 298 in Northumberland, County Durham and Tyne and Wear, more than 130 in Essex, 148 schools in West Yorkshire; 121 in Sheffield and north Derbyshire and more than 100 in Teesside
- Many schools were affected in Northern Ireland and at least 20 were closed in Wales
Drivers have been stuck on the A2 near the M25 in Kent. Truck driver Nigel Waller, who was on his way to Bradford, told the BBC at 0100 GMT that traffic was slowly starting to move.
"I'm doing 15 miles an hour which is the fastest I have driven in hours. I have been stuck since 1730," he said.
"I haven't seen any gritters and it's getting slippery because it's freezing and there's slush. I saw a truck trying to overtake a broken down car - he went straight through the central reservation."
In south London, a surgeon struggling to get to St Helier Hospital in Sutton to operate on a critically ill patient was forced to flag down officers on a routine patrol and request a police car escort.
Motoring organisation the AA said it expected to attend 18,000 breakdowns by the end of Tuesday, bringing the total call-outs since last Thursday to 100,000.
It said London's M25 (J2-J5) was among the worst-affected areas due to falling snow freezing on the carriageways.
The AA's Paul Leather said: "Today has been another busy day and there's more to come this evening as temperatures drop with ice causing big problems across the entire country.
"If you are driving on icy roads, try to minimise the use of brakes to reduce the risk of sliding - keep your speed down, stay in a higher gear to aid traction, anticipate hazards, and keep well apart from other vehicles."
The RAC said it attended about 2,000 breakdowns an hour on Tuesday morning, with some areas up to twice their normal levels for the time of year.
A spokesman said: "The sub-zero temperatures are putting a lot of pressure on car batteries. If possible the car should be kept in the garage.
"Additionally, when starting the car in the morning make sure everything is switched off - including fans, blowers and the radio - then put the key in the ignition and switch to the 'on' position for two to three seconds before starting the engine."
Almost a third of UK rail services had suffered delays by noon on Tuesday, according to the Association of Train Operating Companies (Atoc).
But by early evening the situation had improved slightly, with around 73% of trains arriving on time, it added.
A spokesman said: "Hundreds of workers from operators and Network Rail will work round the clock tonight in Arctic conditions to keep trains running and to make sure that passengers can get to their destination safely."
The Local Government Association said councils had increased stockpiles of salt and grit.