Forecasters escalated weather warnings on Thursday and warned of “risk to life” as many parts of Britain braced for more snow and ice.
The Met Office upgraded its predictions of disruption to amber – which suggests “severe” impact and “potential risk to life and property” – for London, areas of the south west of England, and some parts of Wales until Friday.
“A band of rain will arrive from the south west on Thursday afternoon, quickly turning to snow and becoming heavy at times,” the Met Office said.
“Three to seven cm is likely to accumulate quickly – within two to three hours – with up to 10 cm in some places.”
Yellow weather warnings – which suggest it is highly likely that conditions could cause some disruption – remain in place for much of the rest of England, Wales and Scotland.
Councils were already cancelling transport services, including school buses, ahead of predicted widespread disruption on Friday.
Motorists were earlier warned over the threat of dense freezing fog after Thursday was confirmed as the coldest morning of winter so far.
Drivers were advised to expect delays and be alert to adverse road conditions, especially in central parts, Highways England said.
School closures were reported across Scotland on Thursday, with Highland Council saying at least 11 schools were shut due to disruption on roads.
Pembrokeshire County Council in south-west Wales said four schools would be closing early due to the “forecast for snow and icy road conditions”.
Temperatures plummeted overnight to lows not seen this winter so far.
Braemar in Aberdeenshire was the coldest spot in the country as temperatures dipped to minus 11C (12.2F), 0.2C lower than the previous record for 2019.
All four countries in the United Kingdom set new records for the 2018/2019 winter with Sennybridge, Powys, dropping to minus 9.3C (15.3F), Katesbridge in Northern Ireland falling to minus 8.2C (17.2F) and Redesdale Camp, Northumberland, recording temperatures of minus 10.4C (13.3F).
Met Office forecaster Mark Wilson said earlier that the cold temperatures were due to stick around.
He said: “It’s been a very, very cold night. On Thursday night we could see similar temperatures in Scotland, but Northern Ireland, England and Wales probably won’t be quite as cold.
“Saturday night into Sunday could also be very cold.”
Southeastern Trains said 21 services were being cancelled or altered on Thursday morning to minimise the impact of ice forming on the rails and ensure lines were clear and that it would run its “winter weather timetable” on Friday due to the forecast.
Manchester and Liverpool airports confirmed they were “fully operational” on Thursday morning.
It came after snow forced the airports to close runways for several hours on Wednesday, affecting tens of thousands of passengers.
Wilson added that central England and Wales could bear the brunt of the snow on Thursday afternoon and into the evening as wet weather coming through the south . west England turns wintry, with some places seeing up to 4in of snow.
Yellow weather warnings for ice are in place in north western Scotland and the Northern and Western Isles, alerting travellers to be wary of slippery roads.
A similar warning is in place for north west England, south west England, Wales, Yorkshire and The Humber.
The Midlands, east of England, Greater London and the south of England should also beware of fog making driving on icy roads even more complicated on Thursday morning.
A yellow warning for snow is also in place across large swathes of England and is due to remain in place until late on Friday night.
Most of Scotland should also be prepared for snowfall, the Met Office warned.
This article has been updated throughout.