Temperatures widely dropped to between -1C (30.2F) and -4C (24.8F) across the UK on Wednesday morning, getting as low as -7.8C the Grampians, Scotland, and -7C in Shap, Cumbria.
Further heavy snow fell in northern Scotland overnight, while north Wales and the midlands also woke up to fresh snow on the ground.
Yellow weather warnings are in place for parts of all UK nations.
For much of England, including much of the south and West Midlands, an ice warning is in place until 10:00.
A snow and ice warning along the east coast of England – from East Anglia up to north of Newcastle-upon-Tyne – will be in effect until 12:00.
Most of Northern Ireland and Wales are also under a yellow warning for snow and ice until 10:00.
The Met Office has issued a new yellow warning for snow and ice across parts of northern Scotland and its west coast, which will last from 10:00 on Wednesday until 12:00 on Thursday.
A yellow warning means it is likely that the weather will cause disruption to travel, and there is a danger of slips and falls on icy ground.
In north Wales, trains were suspended between Llandudno and Blaenau Ffestiniog until about 07:30, with delays on the line expected until 09:00.
In Northern Ireland, Translink has warned of disruption to some services in the Magherafelt and Cookstown areas, including school routes, due to road conditions.
ScotRail has said it was struggling to source rail replacement transport due to the weather, after a fallen tree caused disruption to some services in and out of Aberdeen – but tickets are valid on existing Stagecoach North services.
Meanwhile, more than 40 schools in Scotland, almost 50 in Wales and at least 30 in England are shut due to frosty conditions.
More snow is expected in parts of Scotland, north Wales and also over higher ground of eastern England throughout the day, with motorists warned of potential icy conditions.
