Public Health England (PHE) has warned of “severe” cold weather across the country in the coming days.
The Met Office has forecast low temperatures for many parts of England until 9am on Thursday, PHE said in a cold weather alert on Tuesday.
The north-east, Yorkshire and the Humber, the East Midlands, as well as east and south-east England are likely to see “severe cold weather conditions”, PHE said.
Met Office meteorologist Greg Dewhurst said temperatures may drop to minus 2C in East Anglia on Tuesday evening before rising slightly overnight.
He said: “We will continue to see chilly days, and the risk of some frost at night over the next few days, but I would say we are passing the coldest weather now.”
A yellow weather warning for freezing fog is in place until 2am on Wednesday for areas including Norfolk, Essex, Suffolk and Kent.
Dr Ishani Kar-Purkayastha, consultant in public health at PHE, said people should try to heat their homes to at least 18C, particularly those with reduced mobility, are 65 and over, or have a health condition.
She said: “Keep moving too if you can. Get up and walk around and spread housework throughout the day to help keep yourself warm. Food is also a vital source of energy so have plenty of hot food and drinks.
“Remember to check up on frail or older neighbours and relatives at this time, particularly if they live alone, and remember to follow Covid-19 social distancing guidance when looking out for others.”
Wednesday is forecast to be a “chilly day” for the north, east and south-east of England, with maximum temperatures reaching between 5C and 7C.
The mercury is expected to rise only slightly higher in the west to 9C.
Mr Dewhurst said: “Temperatures are a little bit below average for this time of year. The average maximum temperature should be generally around 8C to 9C for this time of year.”
Altnaharra in northern Scotland has seen the coldest day of December so far this year in the UK, with temperatures dropping to minus 9.6C on Friday, Mr Dewhurst added.
The Met Office said areas within the yellow weather warning will see the fog “turn thicker and more widespread this (Tuesday) evening and for a time tonight, although not everywhere will be foggy”.