Some parts of Scotland have been running low on grit
Snow and ice are causing further problems in Scotland and other parts of the UK, with forecasters warning the freezing conditions are here to stay.
Severe weather warnings have been issued for Northern Ireland, Wales, north-west England and Scotland, where some councils have run low on grit.
The extreme weather has closed schools and caused travel delays.
More snow is set to spread across the UK and BBC forecaster Peter Gibbs said few, if any, areas would escape.
Provisional Met Office figures suggest December 2009 was probably the coldest since 1995 across the UK as a whole.
The lowest temperature recorded on Sunday night was -14C in Eskdalemuir, south-west Scotland, while the mercury dipped to -12.6C in Sennybridge in central Wales.
Fife Council became the first to confirm its grit supplies had been exhausted after receiving less than it ordered from suppliers, but 250 tonnes of salt and grit arrived on Monday afternoon.
Cumbria has halted gritting low-priority routes to preserve salt stocks. The county council said the soaring national demand for salt had affected its supply.
Meanwhile, treacherous road conditions have led to the closure of the Giant's Causeway, Northern Ireland's top tourist attraction.
A National Trust spokeswoman said the icy weather had made the north Antrim coast area "extremely dangerous".
'No let up'
The Met Office has issued severe weather warnings for heavy snow and icy roads in Orkney and Shetland, the Highlands and Eilean Siar (Outer Hebrides), Wales and north-west England, with up to 10cm (4in) possible on higher ground.
More snow and ice for UK
It has also issued a warning for widespread icy roads in Central, Tayside and Fife, Grampian, Strathclyde, south-west Scotland, Lothian and Borders, and Northern Ireland.
Sleet and snow will move across Scotland, Northern Ireland and northern England on Monday night, leaving icy conditions in its wake. Temperatures will dip to -8C in Glasgow.
The BBC weather centre said it would be an icy start on Tuesday across the UK, with the snow moving southwards across Wales and much of England during the day.
The Met Office has issued an advisory for heavy snow and widespread ice across much of the UK on Tuesday, with conditions deteriorating in south-west England later in the evening.
BBC forecaster Peter Gibbs said he could see no end to the freezing conditions for at least a week.
We're going to start seeing a very cold easterly wind feeding in direct from Siberia
"It's going to stay cold and perhaps get even colder in parts," he said. "There probably won't be many places that don't see some snow by the end of the week.
"It's also going to be extremely icy on Tuesday morning for many of us, so really very difficult conditions for drivers and the authorities to cope with."
He added: "We can see no let up. By the weekend we're going to start seeing a very cold easterly wind feeding in direct from Siberia."
The bookmaker William Hill has slashed the odds of 2010 being the coldest year on record from 100-1 to 20-1.
Weatherman John Kettley predicted the current freeze would turn out to be the longest spell of severely cold weather since 1987.
"It's not going to be the coldest ever because if you go back to 1963, I mean this sort of wintry weather went on for about 11 weeks," he added.
"That was a proper severe winter and we're not going to get the like of that one again, whether you're calling it global warming, climate change, or whatever."
The freeze, combined with rail delays and a series of accidents of major roads, led to disruption for people returning to work on Monday morning after the Christmas break.
Trains in and out of London's Liverpool Street station were delayed for up to 60 minutes by over-running engineering work and services between Glasgow and Edinburgh were also interrupted by poor weather.
Network Rail said about 75% of trains were running on time on Monday, compared with recent punctuality figures of about 90%.
"The weather has played its part today," a spokesman said. "We've had some faulty trains and the continuing driver shortage on First Capital Connect routes."
By 0800 GMT on Monday, the AA said it had attended about 6,000 breakdowns since midnight, with a total of more than 22,000 expected by the end of the day.
The motoring organisation said that was about two-and-a-half times more than on an average Monday, with many call-outs prompted by flat batteries, frozen engines, or accidents on icy roads.
Curling fans in Scotland played a match on a frozen lake
Fife Council said the "most prolonged period" of freezing weather for 20 years had left grit supplies exhausted.
Grit stocks are "extremely low" in Aberdeenshire but the authorities were expecting a delivery of 5,000 tonnes of salt, while Renfrewshire Council said it was prioritising main routes to conserve its supply.
A spokeswoman from the Highland Council said: "Over the past three weeks, we have used 30,000 tonnes: more than the total for 2006/7".
Scottish Finance Secretary John Swinney told the BBC there was more than 40,000 tonnes of salt available in Scotland on Monday and fresh pre-ordered supplies were still coming into the country.
"The challenge is to make sure that's available in every locality," he said. "There was a problem in Fife and we resolved that problem."
Some minor roads had not been treated as effectively as local authorities would have liked due to the "intensity" of the cold weather, he added.
The Highways Agency said grit stocks in England were holding up.
Meanwhile, thousands of pupils enjoyed an extra day's holiday on Monday as dozens of schools shut due to the wintry weather.
Local authorities confirmed 19 closures in Northumberland, 13 in Lancashire and 12 in Durham.
Schools in Scotland were closed on Monday for a public holiday, and all schools in the Scottish Borders and Dumfries and Galloway will stay shut on Tuesday.
Some schools in Wales are also likely to be closed on Tuesday due to the bad weather.
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