Another day of freezing temperatures and icy conditions, as well as heavy snow in some areas, is set to disrupt travel as the working week begins.
Met Office amber "be prepared" snow warnings suggest 10-20cm could fall in northern England, the Scottish Borders and eastern Scotland.
A yellow "be aware" ice warning covers East Anglia, southern England and south Wales.
The spell of severe wintry weather across the UK is in its fourth day.
In the areas of England and Scotland expecting the heaviest snow on Monday, it would be "blown in on a very strong easterly wind which will just blow the snow around and drift it in places, making for some really poor travelling conditions", said BBC forecaster Ben Rich.
Forecasters also warned sub-zero overnight temperatures would lead to ice forming where snow had fallen or melted during Sunday.
There are particular problems of ice predicted from an area of wet weather due to hit south-west England on Monday morning, bringing rainfall on to frozen ground as it moves across southern England.
In other developments:
- Hundreds of schools have already decided to remain closed on Monday: in the West Midlands, at least 500 schools will stay shut; about 120 are closed in Northamptonshire; there are 93 closures in Surrey; in East Sussex, 89 are closed or partially closed
- Heathrow Airport has reduced its schedule for Monday by about 10% - cutting about 130 flights - in anticipation of low visibility due to the weather
- On the rail network, Greater Anglian predicts "some morning peak cancellations to/ from London Liverpool Street"; South West Trains services are suffering disruption; Southern warns of a "reduced service on some routes between London and the south coast"; and Gatwick Express is running a revised service
- Tributes have been paid to climbers who died in an avalanche in the Scottish Highlands on Saturday
The Met Office has also imposed yellow "be aware" snow warnings for much of the eastern side of England and Scotland as well as Northern Ireland.
John Caldwell, from the Highways Agency, said main roads should be clear of snow.
He added: "Although we've treated the roads consistently throughout the night the roads could still have patches of ice, so those people who do have to drive, we're asking them to keep their speed down, keep the distance between themselves and the car in front to avoid any sharp braking."
He said "hard shoulders and some of the local roads will still be very difficult".
Continue reading the main storyAt about 05:30 GMT on Monday, BBC Radio Humberside reported a number of roads in North Lincolnshire and East Yorkshire where there was 1-3ft of snow and routes were virtually impassable or only open to 4x4s.
Heathrow said the details of flight cancellations would be announced by airlines when they had finalised their schedules.
A statement from the airport added: " It is possible that weather conditions at other European airports will increase the number of cancellations."
On Sunday evening, a number of British Airways flights to Heathrow's terminal five were diverted to other UK airports after BA was unable to de-ice planes on the ground quickly enough to clear the stands.
Heathrow cancelled 300 flights on Sunday, as weather conditions also forced temporary closures of Birmingham Airport and Belfast City Airport to allow snow to be cleared, and led to more than 40 cancellations at London City Airport.
Later on in the week, the BBC Weather centre forecasts further sleet and snow at times, with widespread frost and ice likely.
For more information on the weather and transport situation in your area, visit the BBC Weather website and BBC Travel News.
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