Heavy snow and ice cause disruption across the UK
More snow is expected for many parts of the UK over the next 48 hours ..
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Several UK airports have been closed and train services cancelled after heavy snowfalls in many areas.
Motorists are being urged to take care because of ice, and police in Northern Ireland and parts of Scotland are warning against non-essential travel.
At least 440 schools in Wales, 200 in Scotland and 220 in Northern Ireland are closed.
More snow is forecast later and on Saturday, with up to 25cm (10in) in Wales and southern and central England.
Energy Minister Charles Hendry has warned that more bad weather over Christmas could lead to "very serious" shortages of domestic heating oil.
The Met Office has issued severe weather warnings for widespread icy roads for the whole of the UK and temperatures will struggle to get above freezing everywhere.
There are also warnings of up to 20cm of snow in Orkney and Shetland, Highlands and Outer Hebrides, Grampian, Northern Ireland, Wales and south-west England on Friday.
By Saturday, another band of heavy snow is forecast to affect southern England, the Midlands and southern Wales, with 5 to 10cm likely in many places and 20 to 25cm possible in some others.
Several major roads - including a 50-mile stretch of the A9 in Scotland - and many minor roads are blocked by snow
Police say conditions have been "particularly atrocious" in Caithness, Sutherland and Easter Ross, and some motorists had to be rescued from their cars after becoming stranded
Flights are suspended at Aberdeen, Inverness, Norwich, Exeter, City of Derry, Belfast City and Belfast International airports, and disruption is possible at other airports, including Gatwick and Heathrow
ScotRail, and Arriva and Virgin train services in Wales are experiencing delays and cancellations
Friday's race meeting at Uttoxeter has been abandoned
Friday was due to be the last day of term in many schools, but hundreds have closed their doors early because of the weather.
Continue reading the main story WEATHER AND TRAVEL INFO
Get the latest on travel problems and school closures via your local website
Check if snow is forecast in your area at BBC Weather
Details of motorway and local road closures and public transport disruption are available at BBC Travel News
For advice on handling difficult driving conditions, see the Highways Agency website
For information about severe weather warnings, see the Met Office website
For information about staying healthy in the cold weather, see the NHS Winter Health website
More than 150 in Aberdeenshire, more than 50 in the Highlands, and at least 30 in the Western Isles are among them.
New Scottish Transport Minister Keith Brown has insisted Scotland is "very well prepared" and the authorities are doing all they can to keep trunk roads open.
But the BBC has been contacted by people in the Aberdeen area who have reported atrocious road conditions.
Motorist Kirsty McCullough said: "It took me nearly four hours to do a four-mile round-trip. It's absolutely awful, the roads are sheet ice. They've not been gritted at all."
Mr Brown's predecessor Stewart Stevenson resigned after his department was criticised for its handling of the problems caused by the previous bout of severe weather.
Motoring organisation the AA said it had extra patrols on standby, while Network Rail said it had "snow teams in place" and would be "keeping equipment in strategic locations".
Heavy snowfall during the past few weeks has caused huge disruption, especially in Scotland and north-east England.
Airports, roads and schools were closed, and companies are now warning of a backlog of deliveries which may not reach customers before Christmas.
The Royal Mail is putting on 7,000 delivery rounds this Sunday in a bid to ease the problem.