Wintery weather which has caused road, rail and air travel disruption across the UK is set to continue overnight and into Tuesday, forecasters say.
Provisional Met Office figures show Monday was the coldest day in the UK since December 2010 with -9.3 Celsius (15F) seen at Braemar, Aberdeenshire.
Yellow warnings for snow and ice are in place for northern Scotland, Orkney, Shetland and north-east England.
There is also a yellow warning for ice in south-east England.
As the cold snap continues parents are being warned to tell their children about the dangers of playing near frozen lakes after three boys died in the West Midlands.
The children, aged 8, 10 and 11, died after falling into the lake at Babbs Mill Park, Kingshurst, on Sunday. A fourth boy, aged six, is in a critical condition in hospital after being pulled from the water.
Supt Richard Harris of West Midlands Police said officers were working through the details of what had happened and could not say how long the boys had been in the water before emergency services arrived.
Met Office spokesman Oli Claydon said there will be heavy snow again on Tuesday in parts of Britain, with as much as 15-20cms (6-8ins) accumulating on higher ground.
“In terms of temperature, we could see another very cold night, especially in parts of Scotland where we’ve got that lying snow,” he said, adding that “widespread freezing conditions” were expected.
Mr Claydon urged commuters across the UK to “leave a little bit more time” if driving and to travel with “a bit of extra caution”.
Travel will also be affected by a strike on the railways on Tuesday after the RMT union rejected a pay offer from Network Rail.
Industrial action is expected to affect much of the rail network on Tuesday and Wednesday, with more travellers expected to take to the roads.
Motoring organisation the RAC said it had received more than 9,000 calls from drivers needing roadside assistance – about eight breakdowns every minute – which was “50% more than we’d expect on a typical Monday in December”.
It said people should only drive if conditions allow and if they feel confident to do so, warning drivers to prepare for extremely slippery conditions.
It also urged motorists to carry a blanket and a fully-charged mobile phone when travelling.
Traffic Scotland said ice was affecting driving conditions in the Strathclyde, Lothian and Borders, Central, Tayside, Fife, and South-West regions of the country.
On Monday, many airports around the UK were affected by the weather, with more than 140 flights cancelled because of ice and snow.
London airports – Stansted, Gatwick, Luton and London City – were among the worst affected, while flights from elsewhere in the country were also cancelled due to poor weather conditions.
Steven Facer, from Rutland, told the BBC he and other passengers were left sitting on a Barcelona-bound flight from Stansted for several hours on Sunday night before it was eventually cancelled.
Mr Facer then had a “long drive home in the snow arriving back at 02:00”.
As temperatures drop below freezing councils are urging people to check on vulnerable neighbours, particularly as the cost of living crisis has made it too expensive for some to heat their homes.
The Local Government Association, which represents councils in England and Wales, said that while deaths do rise during normal winter periods, some people were more exposed to the cold this winter.
It said those most at risk were the elderly and people with respiratory conditions, circulatory diseases and dementia, adding that many councils were using libraries or other local venues to provide warm spaces for those who need them.
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