Heavy snowfall blanketed parts of Britain on Monday, disrupting airports, train networks, and roads, while two coal plants were put on standby in case of a power crunch as the country recorded its coldest night of the year so far.
Parts of London's underground network were suspended or faced delays, while motorways were gridlocked due to snow. London's Gatwick and Stansted airports warned flight schedules could be disrupted.
The Met Office issued a yellow weather warning for snow and ice in London and south-east England, with ice and fog warnings in other parts of England and the whole of Northern Ireland.
Temperatures dropped below -15 degrees Celsius (5 degrees Fahrenheit) in northern Scotland, with the Met Office confirming it was the coldest night of the year. Further warnings in Scotland and north-east England for the potential disruption caused by weather will start at midnight on Tuesday.
Meanwhile, Britain's National Grid (NG.L) issued a notification to prepare two winter contingency coal plants.
"This measure should give the public confidence in Monday's energy supply," the power grid operator said, adding it was not confirmed the plants would be needed, but they would be ready.
The snow caused problems for commuters and holidaymakers at the start of a fortnight when rail workers and border officials plan industrial action.
Several train operators advised customers not to travel, while emergency services said it was important people take care in potentially hazardous conditions.
Three boys died and a fourth - aged six - was in critical condition after they fell into an ice-covered lake in Solihull, central England, on Sunday afternoon.
"Searches of the lake are continuing as we seek to establish exactly what happened and if anyone else fell into the water," West Midlands Police said.
