Snow and ice warnings have started to kick in for large parts of the country, as forecasters expect "one of the coldest weeks of this winter so far".
The Met Office has warned the mercury could plummet as low as -7C in some parts of the UK this week, while the bulk of the population can expect to shiver through sub-zero temperatures.
About 1cm to 3cm of snow could accumulate inland, mainly over hills above 100 metres, with up to 5cm predicted above 200 metres.
The first of a series of yellow weather warnings for ice and snow is in place for southeast England, London, and east England until 10am on Monday.
The second is an ice warning affecting the East Midlands, east and northeast England and Yorkshire and Humber, also until 10am today.
A third snow and ice warning affecting Scotland, Wales, West Midlands and Yorkshire and Humber begins at 8pm on Monday and continues until 3pm on Tuesday.
Experts say ice is expected to develop across western Scotland and Northern Ireland during this period.
A fourth yellow warning comes into play from 5am on Tuesday until 9am on Wednesday affecting the Highlands, Northern Ireland, southwest Scotland, Lothian and Borders, Strathclyde, Wales and southwest England.
The cold snap is expected to grip Britain until at least next weekend, with the chance that milder weather may not arrive until the middle of the following week.
Met Office forecaster Craig Snell said it would probably be "one of our coldest weeks of this winter so far".
More from Weather
He added: "It's going to be a very cold spell across the UK and our message is to allow some extra time for your journeys.
"Untreated surfaces will be prone to some ice and there could be some disruption to travel."