A health warning has been issued to urge people to be prepared for icy conditions as parts of South-east England are set to be colder than Iceland.

As temperatures are set to reach lows of -6C overnight, Public Health England has warned people to be prepared as “cold does kill”.

London woke up to a severe frost on Tuesday as the temperature dropped to just 3C over the course of the day – making it colder than the Icelandic capital of Reykjavik.

Dr Angie Bone, from the extreme events team at Public Health England, said: “Cold does kill, even in places where the temperatures are not at their lowest.

“Now is the time to prepare for the cold weather forecast by the Met Office, and to think of those you know who are older, very young, or have pre-existing health conditions who are particularly vulnerable.”

It has advised people to keep the heating on, saying optimal indoor temperatures should remain at around 18C and said that people should look out for family members and friends who may be particularly vulnerable to the cold and should stock up on food and medications in advance.

Andy Page, Chief Operational Meteorologist at the Met Office, said: “High pressure will bring generally dry and settled conditions this week, with clear skies and light winds allowing a widespread frost to occur on Monday and Tuesday night.

“From Wednesday onwards cloudier and slightly less cold conditions will arrive across northern England, therefore overnight frosts will become fewer and less severe in the north but cold weather may persist across the south where skies remain clearer.

In pictures: Winter weather hits the UK Show all 17 1 /17 In pictures: Winter weather hits the UK In pictures: Winter weather hits the UK A man works in the snow in the Yorkshire Dales near Hawes In pictures: Winter weather hits the UK A man jogs past the partially frozen Sefton Park Lake in Liverpool PA In pictures: Winter weather hits the UK A jogger runs through the snow under the Angel of the North in Gateshead, Tyne and Wear PA In pictures: Winter weather hits the UK A man walks through the snow close to the Angel of the North in Gateshead, Tyne and Wear PA In pictures: Winter weather hits the UK Temperatures drop as night time falls and snow blankets moors in the Peak District near Buxton Getty Images In pictures: Winter weather hits the UK Temperatures drop, as night time falls, and snow enhances the complex pattern of fields on the moors in the Peak District near Buxton Getty Images In pictures: Winter weather hits the UK A van waits to be recovered after sliding into a ditch on an icy road in the Peak District near Buxton Getty Images In pictures: Winter weather hits the UK Snow blankets the countryside in the Peak District near Buxton Getty Images In pictures: Winter weather hits the UK Farmers on the Richmondshire and Cumbria border take feed for the sheep on the Pennine tops with the A66 trans Pennine route in the background as snow falls across many parts of the UK PA In pictures: Winter weather hits the UK A tractor with a snow plough parked outside the Tan Hill Inn in Swaledale, North Yorkshire as snow falls in the Pennines PA In pictures: Winter weather hits the UK Cars make their way through the snow on the A1 northbound in Gateshead, Tyne and Wear, as the UK braced for a new wave of bad weather after forecasters issued warnings of heavy snow in parts of England and Scotland PA In pictures: Winter weather hits the UK Snowfalls over high ground of the Pennines at Tan Hill PA In pictures: Winter weather hits the UK Sue and Chris Betts take their dog for a walk in the snow near Beamish, Tyne and Wear after heavy snow in the area PA In pictures: Winter weather hits the UK Clyde Wind Farm near Abington in Scotland PA In pictures: Winter weather hits the UK Sheep near Abington in Scotland PA In pictures: Winter weather hits the UK Snow in Abington in Scotland as the cold weather hits parts of the UK PA In pictures: Winter weather hits the UK Snow blankets the countryside in the Peak District near Buxton Getty Images

“Looking ahead into December and beyond, there are indications that a cold start to winter is more likely than normal, but this doesn’t guarantee snow nor does it mean we won’t see spells of mild and wet weather at times.”

Forecasters have put the icy weather down to a meteorological phenomenon called a “polar vortex” which has come down from the Arctic and will increase the risk of a cold snap “between now and Christmas”.