He is chairing a ministerial meeting at the Cabinet office of ministers and agencies to discuss responses to the severe weather.
The weekend could be colder, with Arctic conditions forecast to last at least another week.
Motorway hard shoulders are no longer being gritted, with the government prioritising salt for the worst-affected regions.
Supplies have been close to running out in some areas, with many councils restricting gritting to major roads.
Thieves using a lorry with heavy-lifting gear stole a grit bin with two tonnes of salt intended for streets and footpaths from a road in Newton Mearns outside Glasgow.
Milk deliveries have also been disrupted, with tankers struggling to reach dairy farms.
Some farmers have had to dump supplies as few have large storage facilities while, in Scotland, several barn roofs have collapsed under the weight of snow.
Electricity suppliers say "a few hundred" homes in southern England are without power, after 5,000 were cut off by weather-related problems on Thursday.
Thousands of schools remain shut, with exam candidates in England, Wales and Northern Ireland warned they could have to wait five months to sit GCSE and A-level modules if weather prevents them taking them next week.
Exams watchdog Ofqual said in cases where candidates would not have a second chance to sit papers in the summer, applications could be made for "special consideration".
WEATHER AND TRAVEL INFO
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Details of motorway and local road closures and public transport disruption are available at
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For information about staying healthy in the current cold snap, see the
NHS Winter Health
This involves pupils disadvantaged by circumstances being awarded up to an extra 5% of the maximum marks.
The Department for Children, Schools and Families insists schools should stay open "wherever reasonably practicable" during severe weather.
A spokesman said the focus of government concern was solely on persistent, unauthorised absence and it was up to head teachers to use common sense as to whether to authorise a child's absence in severe weather.
Travel problems persist, with passengers advised to check their flight's status before going to the airport:
Easyjet cancelled about 30 flights at airports including Gatwick, Liverpool, Belfast and Stansted. All airports are now open, though suffering from widespread delays
British Airways said it had asked passengers on some flights arriving at Heathrow's Terminal 5 to leave without their luggage, with bags being sent on to them later
Train companies operating revised timetables include East Coast, ScotRail, First Great Western, South West Trains, Southern and Southeastern, while Eurostar has cancelled several services
Rail passengers travelling through Birmingham are being delayed by up to two hours because of signalling problems at New Street. This affects some Virgin Trains, Arriva Trains Wales, CrossCountry, London Midland and Wrexham and Shropshire services
The outside lane of the M40 was closed for much of its length throughout Oxfordshire due to snow and ice, and the A3(M) in Hampshire faced northbound restrictions between junctions three and two
In north-east England, there are delays on the southbound A1(M) near Washington after a crash caused the closure of one lane
The RAC said its patrol teams had attended 5,000 call-outs by midday on Friday and 250,000 since the cold weather began on 18 December.
The organisation said it was receiving about 1,500 calls an hour - more than twice as many as normal. The busiest areas today were Manchester and the Wirral, Scotland, the West Midlands and Wales.
Meanwhile, Environment Secretary Hilary Benn has insisted there are "plenty of supplies" of gas, with storage about 70% full, and that domestic customers need not worry.
Hardy swimmers take the plunge in icy water at the Serpentine in London
Some 27 firms - 12 in the East Midlands and 15 in the North West - are still using alternative fuels after National Grid triggered a clause in their contracts to turn off gas supplies at times of high demand.
At one stage on Thursday, 95 major firms were affected.
The Met Office recorded the UK's lowest temperature on Friday morning in Altnaharra, Sutherland, while England's low was -17C (1.4F) in Woodford, Cheshire.
Sennybridge in Powys was the coldest place in Wales at -14.7 (5.5F), while Northern Ireland's low was -11.1 (12F) at Lough Fea, County Tyrone.
In Bristol Harbour, the temperature was low enough that the sea began to freeze over.
The lowest ever recorded temperature in the UK was -27.2C (-17F) in Braemar, Aberdeenshire, in 1895 and 1982, and in Altnaharra in 1995.
Temperatures are expected to stay around freezing throughout Friday and forecasters say winds could make it feel even colder.
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