Temperatures are expected to plummet this weekend, putting further strain on the NHS.
A yellow warning for icy conditions has been issued by the Met Office for parts of the northeast of England and Scotland, and in Cornwall, Devon and Somerset.
Temperatures are forecast to fall on Saturday night due to “cold air and clear skies”.
A Met Office spokesman said that across parts of Scotland temperatures could drop as far as -10C (14F), which is much colder than average for the time of year.
NHS England urged people to stock up on medicines, check on vulnerable or elderly neighbours and get the flu jab.
The comments came after it emerged that tens of thousands of planned operations could be delayed for at least a month, as the norovirus and rise in flu levels put pressure on hospitals.
A spokesman said: “Freezing conditions are forecast in some areas and evidence shows that the risk of heart attacks, strokes and other serious breathing problems increases as temperatures plummet.”
He added that two-and-a-half times as many flu sufferers have been admitted to hospital than at this point last year.
And Dr Nick Scriven, president of the Society for Acute Medicine, said a “real crisis” had developed since New Year’s Eve.
He said: “There has been debate as to what constitutes a crisis but to all those working at the front door the last four days has definitely been at that level.
“The temperature is set to drop again and looks like it will be below the 5C mark, which statistics show means more illness and more hospital attendances to come.”
He added that while some of the claims by medics had been “overzealous and hyperbolic”, he urged the Government to listen to doctors’ concerns and act on them.