Temperatures could reach their lowest so far this autumn, with a frosty night ahead, the Met Office has warned.
Fog patches are also expected to form across central and south-east England, and in eastern parts of Wales.
On Sunday night, temperatures equalled the lowest of the autumn so far, reaching minus 8.1C (17.4F) in Tulloch Bridge and Dalwhinnie in Scotland.
In Northern Ireland the lowest temperature recorded was minus 5.1C (22.8F) in Katesbridge, County Down.
The Met Office said Monday night would be cold and frosty for many areas and could be the coldest night across the UK as a whole.
Locally, temperatures could drop as low as minus 9C (15.8F) in rural Scotland and minus 7C (19.4F) in parts of England and Wales.
A Met Office spokesman said the current cold spell may soon come to an end, with temperatures recovering throughout the week.
Public Health England (PHE) has also issued a cold weather warning from 9am on Monday until 12pm on Wednesday.
Dr Emer OConnell, a consultant at PHE, advised people to look out for anyone who may need help staying warm.
“Older people and those with heart and lung problems are at risk of getting sick in cold weather,” she said.
Last night it fell to -8.6 Â°C at Tulloch Bridge, Inverness-shire making it the coldest night of the season so far. It will be very cold again tonight, but overnight temperatures should climb through the week pic.twitter.com/QdvPYowmAe— Met Office (@metoffice) November 18, 2019
People across the UK can expect sunshine on Monday and temperatures will rise across the board, reaching 5C (41F) to 6C (42.8F) in the north and peaking at 8C (46.4F) to 10C (50F) in the south.
Throughout the week, more cloud will push through in the south-west from the Atlantic, bringing an increasing chance of rain.
There is also a chance of showers along the North Sea coast and in the far east of Scotland.