The government has issued its cold weather plan as the Met Office puts out a level two cold weather alert for London, the South East and other parts of Britain.
Will Lang, chief forecaster at the Met Office, said cold air would spread across the UK "in marked contrast to the recent mild weather", bringing sleet and slow.
Dr Angie Bone, part of the extreme events and health protection team at Public Health England (PHE), warned that a "significant change" in temperatures was coming and urged the public to remember "that cold does kill, even in places where the temperatures aren’t at their lowest".
She added: "Our advice is that when indoors, have plenty of warm food and drinks to stay warm and try to maintain indoor temperatures to at least 18°C, particularly if you have to sit still for long periods, have long term illness or are 65 or over.
"Before bad weather arrives is a good time to think about how the bad weather may affect your friends and family, particularly if they are older or very young or have pre-existing health conditions. These groups can be particularly vulnerable to the ill-effects of cold so think now what you could do to help - if you, or they, are eligible for a flu vaccination make sure you get it as soon as you can."
The government's Cold Weather Plan for England sets out a series of actions that health and social care organisations, voluntary and community groups, and individuals can take and plan for cold temperatures to help reduce cold-related illnesses and deaths.