Health authorities have warned people to look out for the vulnerable as severe cold sets in across large parts of the country.
A cold weather alert is in place until 6pm on Tuesday as night-time temperatures plunge to -7C.
Last night temperatures sank to -7C in North Yorkshire, while Oxfordshire and parts of Northern Ireland sank below -6C.
It was Northern Ireland’s coldest night of the winter so far.
Met Office forecasters say there is a 70 per cent chance of severe conditions from tonight, and expect temperatures to fall to -7C in rural parts of southern England and wales.
If fog clears, daytime temperatures will rise back up to a more typical range of 5 to 8C.
By Wednesday morning, clouds moving in from the North will push the cold to the south and reduce temperature extremes, the forecasters added.
Public Health England (PHE) has warned that older people and those with heart and lung problems are particularly at risk of getting sick in cold weather.
It said heating homes to at least 18C is important because below this temperature, changes to the body mean that the risk of strokes, heart attacks and chest infections increase.
PHE’s Dr Owen Landeg, said: ‘Keep an eye out for those who may need help staying warm, ensure they wear lots of thin layers and have everything they need.’
Nick Silkstone, Deputy Chief Meteorologist at the Met Office said: ‘High pressure is in place across the UK this weekend bringing settled, mainly dry, but also cold weather for many.
‘It will be colder than of late with temperatures dropping below freezing overnight and a chance of widespread frost but with sunny spells throughout the day.
‘However, at the start of next week the chance of fog and cloud will increase across central and southern areas which will mean that it will also feel colder by day.’
Parts of Britain are still dealing with the aftermath of Storm Brendan, which caused road closures and rail disruption along with gales of up to 80mph.
Roads and quaysides were flooded this week while workers cleared up torn-off roofs and collapsed scaffolding in Slough and London.
Last month, temperatures of 18.7C near the northern tip of Scotland broke the UK record for late December.