Police are warning people not to travel in areas covered by an upgraded severe weather warning after 200 motorists were left stranded.
Heavy snow and ice caused treacherous driving conditions and brought the M74 in Scotland to a standstill.
Satellite image shows almost half of Britain covered in snow and cloud (NEODAAS/University of Dundee)
The Met Office has issued a fresh amber “be prepared” warning of heavy snow for southern Scotland and northern England on Wednesday into Thursday.
Dozens of schools have been closed in parts of Scotland, while public transport has been disrupted by the weather.
Scotland’s transport minister Humza Yousaf told MSPs at Holyrood that following a new Met Office amber warning for Wednesday evening, Police Scotland were upgrading their travel warning from stage three to a stage four.
He said: “That in practice means that all travel should be avoided on those parts of the trunk road affected by the amber warning, namely south and south-west Scotland for the duration of the amber warning.”
Police Scotland closed parts of the M74 in Lanarkshire in both directions due to wintry conditions for a number of hours overnight. The road later reopened.
Elsewhere a runaway lorry slid down a snowy street then crashed into a fence on Tuesday morning in Glenmavis, North Lanarkshire.
Witness Niki Blackhall, who filmed the incident, said: “The men in the truck got out to help the crashed cars and the truck slid away.
“It hit our wall. I’m just glad nobody was injured and the wall stopped the truck from sliding down the hill, as the outcome would have been a lot worse.”
Mountain rescue teams were drafted in to check on drivers on the M74 overnight, many of whom were stuck in their vehicles for several hours.
Transport Minister Humza Yousaf has apologised to those stranded in their vehicles overnight.
Sam Sykes, a surveyor from Biggar, South Lanarkshire, said he was stuck on the M74 for around 12 hours – from 6pm on Tuesday until around 5.30am on Wednesday.
The 25-year-old was travelling from Dalry in Ayrshire to Biggar after work.
He said: “The length of time, the cold and the uncertainty of when it would start again was the worst part.”
Mat Jackson, 29, a product manager with Siemens, arrived home in Manchester at around 11.30am on Wednesday – having left Glasgow at 3.20pm on Tuesday.
He told the Press Association: “Every time gritters went by you thought ‘here we go’ but the snow just came down harder, it was that thick you couldn’t see in front of you.”
(PA Graphics)
Police declared a critical incident and said that more than 200 people were stranded.
All schools in the Borders were closed due to the weather while 16 secondary schools, 58 primaries and 44 nurseries in the Highlands were shut.
Around 20 schools in Dumfries and Galloway and 28 schools and nurseries in South Lanarkshire were also closed.
All prelim exams scheduled to take place in North Lanarkshire secondary schools on Thursday have also been postponed.
Public Health England issued cold weather alerts and health warnings in light of the cold weather, urging people to take extra care.
The Met Office amber warning advises that travel disruption is likely, with a risk that some vehicles may be stranded.
The warning, which runs from 9pm on Wednesday until 5am on Thursday, says that 3-8cm of fresh snow is likely to accumulate widely, with up to 20cm over high ground.
Yellow “be aware” warnings of snow and ice for much of the country are valid until Friday.