An amber cold health alert has been issued as doctors fear an increased risk of heart attacks, strokes and chest infections.
The Met Office has also issued a yellow weather warning for ice from 4am this morning across London and the South East with more than an inch of snow possible.
Many regions still coping with flooding in the aftermath of Storm Henk will be blasted by the freezing weather.
While much of the week is set to be dry and sunny, snow and sleet is forecast in the South and on higher ground with a bitter bite to the air across England and Wales.
The health amber alert – cautioning that the impact could be felt across the health service with potential for the population to be at risk – was issued for the North West, West Midlands, East Midlands and South West by the UK Health Security Agency and the Met Office, running until noon on Friday.
A yellow cold health alert – where the impact could hit vulnerable populations and an increase in risk to health for those over the age of 65 or with health problems – is also in place for the North East, Yorkshire and The Humber, East and South East of England.
Dr Agostinho Sousa, head of extreme events at UKHSA, said: “Cold weather can have a serious impact on health.
“If you have a pre-existing medical condition or are over 65, it is important to try to heat the rooms where you spend most of your time, such as your living room or bedroom.”
The Met Office said the North Downs in Sussex would get the most snow with more than an inch falling. Forecaster Marco Petagna said the worst of the cold weather would be on the hills in the North and in Scotland where there are the lightest winds overnight and where temperatures could get “to -6C or -8C”.
He added: “Frost won’t be as widespread or severe in the second half of the week. Wintry showers are coming from the East while the fog will be more likely in the North where there is less breeze.”
Meanwhile, the Environment Agency has warned more properties are expected to flood over the next week as river levels increase.
Some 1,800 homes have been deluged already with properties around the rivers Trent, Severn and Thames most at risk in the coming days.
Local groundwater flooding is also possible in the South of England, Yorkshire and The Humber.
There are still 170 flood warnings in place. The devastation from Storm Henk – largely across Oxfordshire, Nottinghamshire and Gloucestershire – has sparked calls for the Government to review flood defences.
Rishi Sunak visited residents and EA workers in Oxford yesterday, saying: “Flooding has been having a devastating impact on communities up and down the country.”
The PM added more than 1,000 Environment Agency personnel are on the ground and the Government will invest £5.2billion in defences.
