Ice warnings for many parts of UK
Warnings of widespread ice are in place for many parts of the UK, and forecasters say it will continue to be the major problem into the weekend.
Rain, sleet or snow will hit most areas and become icy in the sub-zero temperatures. In some places, daytime temperatures have plunged to -8C.
The weather has continued to cause disruption, with some train services cancelled and many flights delayed.
Two pensioners have been found dead in their gardens in Cumbria this week.
This weekend's sporting schedule, from football to horse racing, has fallen foul of the severe weather.
Scotland is worst hit, with all Premier League football off, and many Football League fixtures have been postponed in England.
Meanwhile, walkers and skiers in the Pentland Hills and on Arthur's Seat in Edinburgh have been warned to avoid slopes laden with heavy snow because they might trigger avalanches.
Snow showers have eased in many areas but the Met Office has issued a severe weather warning for heavy snow for Cumbria and parts of south and mid-Wales. Between 5-10cm (2-4in) of snow is likely over the hills.
Widespread ice warnings have been issued for the Highlands and western Scotland, Northern Ireland, Wales, north-west England, the Midlands, eastern England, the South West, London and the South East.
Friday brought another day of disruption to schools and the travel network, with millions of travellers' plans thrown into chaos because of continued snowfall and freezing temperatures.
Gatwick Airport has reopened after being shut for two days but delays continue, and passengers are being told to check with their airline before leaving home. The Gatwick Express train is suspended but there are other rail options.
Southern and Southeastern rail have reduced services, trains in East Yorkshire are cancelled, and there are virtually no services north of Glasgow and Edinburgh.
As of 1300 GMT, 28% of rail services were not running, and of those operating only 53% were running on time. The Association of Train Operating Companies said services in south-east England and Scotland were the hardest hit.
Overnight, temperatures fell as low as -20C in Braemar, -10C at Manchester airport and -10 in Yeovil.
The thermometer at RAF Leeming in North Yorkshire was showing -17.9C on Friday morning, making it the coldest night recorded at the station since records began in 1945. The daytime temperature at Leeming was -8C.
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The AA said it had attended about 17,500 breakdowns across the UK by 1700 GMT - up from about 16,000 on Thursday. A typical Friday, normally the organisation's quietest day, brings about 9,500 call-outs. The busiest areas are Glasgow, Edinburgh, Newcastle, Leeds and Bradford.
Darron Burness, head of AA special operations, said: "Road salt is less effective from -5C and barely effective at all from -9C, so even main roads were badly affected in places.
"Ice will remain the biggest risk facing drivers over the next few days until we've had a sustained period of milder weather. It's virtually impossible to spot black ice, so keep your speed down and if it's slippery, maintain a 10-second gap between you and the vehicle in front."
The Independent Petrol Retailers Association claimed up to 500 independent petrol retailers in Scotland and the east of England risked running out of petrol and diesel by the weekend. Filling stations in rural areas away from the main trunk roads were particularly vulnerable, it added.
Transport Secretary Philip Hammond chaired an hour-long meeting on Friday morning to discuss the cold spell. Several government departments were represented, as was the Scottish Government, the Met Office, and Local Government Association.
Our political correspondent Iain Watson said it was agreed that while the strategic road network was largely open and there were no major problems with health, gas supplies, or food and petrol distribution, there were some "local issues".
It was said the UK was in a "better position than last year", when supplies ran out in some areas.
There are 1.2 million tonnes of salt held by local councils in England, a national reserve of 250,000 tonnes and more salt has been ordered. England's Highway Agency has 260,000 tonnes of salt compared with 227,000 this time last year.
No decision was taken as to whether rail firms should be fined for making widespread cancellations.
Labour leader Ed Miliband said the government needed to have a "co-ordinated response" to get road and rail services moving as quickly as possible.
In other developments:
- Southern trains, which operates in south London, along the south coast and between central London and the south coast, said that it would be operating a revised timetable on Friday - with half-hourly services in most cases. It has urged Friday commuters to ensure they have begun their journeys by 1930 at the latest due to the "substantial risk of ice on the electric rail"
- First Capital Connect also has a limited service in operation and has warned there will be no trains between Brighton and London after 1930. Other journeys should expect restrictions, delays and cancellations.
- Southeastern trains, which runs out of London Victoria and Charing Cross into Kent and the South East, said it was operating an extremely limited number of services from an emergency timetable
- National Rail Enquiries has set up a hotline for information about snow-related disruption on 08453 017 641, and also has updates at @nationalrailenq on Twitter
- Police forces in Kent and Surrey continued to advise drivers to travel only if necessary as the low temperatures turned snow into ice
- Eurostar cancelled 17 trips on Friday and said its timetable would be significantly reduced, with cancellations and delays, until Sunday
- No trains are running between Cleethorpes and Doncaster, Lincoln and Grimsby and between Lincoln and Doncaster. The line from Bridlington to Scarborough is still blocked.
- Several airports were closed on Friday morning but Guernsey Airport, Jersey Airport, Southampton Airport and Bournemouth Airport have all reopened. Robin Hood Airport, in Doncaster, will remain closed until 1000 GMT on Sunday.
- Many schools were closed again in Scotland - including all schools in Fife, East Lothian, Midlothian, West Lothian, North Lanarkshire and the Borders - and more than 2,000 were closed in England.
Police in Cumbria are investigating the deaths of two elderly people, who died in their gardens in freezing conditions in separate incidents.
Officers said it appeared 80-year-old Lillian Jenkinson, who was found dead in Workington on Wednesday morning, might have fallen in her garden in freezing conditions.
On Tuesday, 84-year-old William Wilson was found dead in his garden in Waitby, near Kirkby Stephen, and police - who are urging people to look out for each other in the cold weather - are trying to work out whether a fall or a medical condition may have contributed to his death.
On Thursday night, a 57-year-old man died after he was hit by a Land Rover Freelander which skidded on ice on the A6108 at Bellerby, North Yorkshire. The victim had gone to help a driver whose car had crashed.
An active search by mountain rescue team volunteers for missing fell walker Gwenda Merriot, 60, from Wiltshire, has ended, but posters are being put up and hotels and B&Bs are being contacted.
She was last seen in Ambleside in the Lake District on Wednesday morning and there has been heavy snowfall since then.