Temperatures dropped to -11C (12.2F) in parts of the UK in the early hours of Thursday, making it the coldest night of winter so far.
The country's lowest temperature was recorded in Braemar, Aberdeenshire.
Met Office yellow weather warnings for snow, ice and fog remain in place for Thursday and Friday.
Southeastern Trains said 21 trains were being cancelled or altered on Thursday morning to minimise the impact of ice forming on the rails.
It added it would run its "winter weather timetable" on Friday - with passengers warned of peak services being busier than normal.
England, Wales and Northern Ireland also recorded their lowest temperatures of the winter so far - with Redesdale Camp, Northumberland, falling to -8.2C (17.2F), Sennybridge, Powys, dropping to -8.1C (17.4F) and Katesbridge in Co Down falling to -6.3 (20.7F).
A bit late to the party, but #Scotland has had its coldest night of the winter so far as well. This makes it the UK's coldest night of the winter
End of Twitter post by @metoffice
What's the forecast?
Media captionSevere weather is expected to continue across the UK
Thursday morning is likely to be "the coldest start to the winter so far", says BBC weather presenter Simon King.
Much of the country will see temperatures well below freezing, with -14C (7F) possible in rural Aberdeenshire, he says.
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Freezing fog is also expected in central areas and snow is forecast for parts of southern England and Wales, he says, reaching depths of 10cm (4in) in parts of Wales and up to 6cm (2in) elsewhere.
He warned to expect "widespread and potentially significant disruption because of that snow" on Friday morning.
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What warnings are in place?
In much of England and Wales, there's a yellow Met Office warning for snow and ice between 13:00 GMT on Thursday and 21:00 on Friday, while eastern Scotland is also expected to be affected, starting later on Thursday.
The Met Office says there is a small chance of travel delays on roads, railways and at airports, and hazardous icy conditions on roads and pavements as temperatures drop below freezing.
There is also a slight chance that some rural communities could be cut off and a "small chance" that power cuts may occur and mobile phone coverage could be affected, the Met Office adds.
Biggin Hill Airport, to the south of London, saw a dusting of snow
Snow and ice caused travel delays and closed hundreds of schools in much of the UK on Wednesday.
In Wales, a climber with a broken leg was airlifted off Snowdon after an avalanche.
Media captionThe avalanche on Snowdon hit a party of climbers
Manchester and Liverpool airports closed runways in the morning but reopened them later in the day.
In Devon and Cornwall, police said they dealt with more than 20 collisions and other road incidents in just one hour on Wednesday morning, most of which were in Devon.
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In Scotland, the driver of a gritting lorry was taken to hospital after his vehicle overturned
