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Forecaster Simon King says cold weather is expected to last into next week
Thousands of people on the lowest incomes in over 300 postcode districts will receive a £25 Cold Weather Payment as temperatures plunge below zero.
Temperatures went as low as -9.1C (15F) in the Scottish Highlands and -8.9C in Cumbria, overnight figures showed.
A cold weather alert for England will run until 09:00 GMT on Monday.
It is issued by the UK Health Security Agency (UKHSA) when the weather is cold enough to be likely to affect people's health.
As parts of the UK are hit by freezing conditions, a fuel poverty charity has called on the government to provide more support for "those at greatest peril".
The government has triggered Cold Weather Payments for eligible people across large parts of England and Wales. It is paid once in a seven-day period and people can check if they will receive it online.
The payments will be made in parts of Cumbria, North East and North West England, West Yorkshire, Greater Manchester, Birmingham, Coventry, Staffordshire and Brecon.
In Scotland, those on low incomes and benefits may receive a one-off Winter Heating Payment, but this is not tied to temperatures.
Current forecasts predict unseasonable temperatures – well below average for the time of year – in many places, with the cold weather continuing into next week.
Heavy snow has been causing traffic disruption across the north east of Scotland, with reports of vehicles becoming stuck on some routes.
The wintry weather also caused delays to flights at Aberdeen Airport, with bus services also facing disruption.
National Energy Action says people are struggling to heat their homes as a result of "impossibly high prices" and they now face "dreadful consequences".
CEO Adam Scorer said "millions have been dreading the onset of winter" and people are choosing between "either huge debt or an unheated home".
"Despite the current programme of support, the government must step in with more help for those at greatest peril this winter," he said.
The Met Office has several weather warnings in place – including across the western and eastern coasts of England and Wales, parts of Northern Ireland and northern Scotland/
More widely, temperatures dipped to about -6C and -7C across much of the UK overnight.
BBC Weather presenter Chris Fawkes said the cold weather would last well into next week as the high pressure over Greenland continues to push cold Arctic air across the country.
"Snow showers will continue to affect north and east Scotland" on Thursday afternoon, he said.
A few centimetres of snow is also expected to accumulate in the north east of England.
The Met Office weather warnings in place include:
Temperatures could plummet to -10C on Thursday night, with a risk of slippery surfaces caused by hard frost, following the quick drop in temperature.
The Met Office has warned people to take care on the ice, with the risk of injuries and slips on icy surfaces heightened on Thursday morning.
In Sheffield, hundreds of homes are still without a gas supply after water leaked into the mains six days ago.
Josh, 30, who lives with his girlfriend and two children in Stannington, is one of those affected.
As he tucked his four-year-old son into bed on Tuesday, Josh wrapped him in five quilts. By midnight he said the house felt "as cold as Iceland" and he spent an hour with a tiny electric heater trying to warm the boy's room.
"Still that wasn't enough," Josh said. "He woke up at half five this morning, crying, cold. What more can we do?"
There are concerns the situation could last until the end of this week and "maybe longer" before gas is restored to everyone.
The UKHSA has reiterated its long-standing advice for people who cannot heat every room – saying they should warm the living room during the day and bedrooms just before going to sleep, ideally to at least 18C.
The cold weather alert for England also requires health care providers to activate special plans, such as arranging gritting services to allow access to critical services and to cover pedestrian hotspots.
But many local councils in England and Wales – who have collectively stockpiled 1.4 million tonnes of salt for this winter – said they were struggling to attract and retain gritter drivers.
Motorists are being advised to keep warm clothes, blankets and flasks of tea in their vehicles. The RAC said people driving in frosty, icy conditions should prepare to keep warm in the event of breakdowns, which are expected to surge this week.
An emergency protocol in London has been activated to provide extra accommodation for rough sleepers.
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UK weather: Freezing conditions trigger cold weather payments – BBC
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