Icy winds from the North Pole are sweeping across the country as Britain prepares to face some of the coldest weather so far this year.
On Tuesday Britain was buffeted with high winds - with more to come
Temperatures could plummet to -15C (5F) in northern Scotland, with 20cm (about 8in) of snow in parts.
Overnight, temperatures fell to -6C (21F) in Sennybridge, in the Brecon Beacons National Park in Wales.
Northern Ireland, Wales, Scotland and south-west England all saw snow fall overnight, with more predicted.
Up to 5in (12cm) of snow fell on high ground in Northern Ireland, with snow falls particularly heavy in the north and west, as temperatures dropped to about -3C (26F).
In Wales, snow falls across many parts overnight meant an unexpected St David's Day holiday for schoolchildren.
Hundreds of schools in Scotland have been forced to close for a second day as blizzards and freezing temperatures hit northern parts.
Temperatures in Scotland during daylight hours were unlikely to rise above freezing, the BBC Weather Centre said.
Care on roads
A number of trains have been cancelled in south Wales and commuters were warned to expect delays.
Police forces across Wales and Scotland were reporting treacherous road conditions, and motoring groups were warning drivers to take extra care on the roads.
It comes after snow and strong winds buffeted northern parts of Scotland, northern Ireland and eastern English areas including Lincolnshire and East Anglia on Tuesday.
The Met Office said further snow was likely on Thursday and Friday.
The Highways Agency said gritters had been working overnight to treat motorways and other major roads.
"Drivers are advised to slow down and leave plenty of room between vehicles, as it can take up to 10 times longer to slow down or stop in wet or icy conditions," said a spokesperson.
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