Temperatures dropped to -13C (8.6F) 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 Loch Glascarnoch in the Scottish Highlands.
Met Office yellow weather warnings for snow, ice and fog remain in place for some of Thursday and Friday.
More snow is forecast overnight, with up to 15cm (6in) possible in some parts of Wales.
In southern England, there could be 3-7cm (1-3in) of snow.
Southeastern Trains said 21 trains were being cancelled or altered on Thursday morning to minimise the impact of ice forming on the rails and ensure lines were clear.
It added it would run its "winter weather timetable" on Friday - with passengers warned of peak services being busier than normal because of changes to some train times.
England, Wales and Northern Ireland also recorded their lowest temperatures of the winter so far - with Redesdale, Northumberland, falling to -10.4C (13.3F), Sennybridge, Powys, dropping to -9.3C (15.3F) and Magilligan, County Londonderry, falling to -8.5C (16.7F).