Thermometers are due to nudge the -8C (17.6F) mark tonight with similar temperatures on the cards tomorrow night.
It comes after England shivered in the coldest night of autumn so far on Monday as the mercury sank to -7.5C (18.5F) in South Newington, Oxfordshire.
Although it will turn slightly milder towards the end of the week the Arctic freeze will tighten its grip at the weekend, experts say.
The early winter blast has sparked warnings to the elderly and vulnerable to take extra care as cold weather can kill.
The Met Office with Public Health England (PHE) has issued a level-2 cold weather alert warning of an increased health risk to some people until Friday afternoon.
Dr Angie Bone, of PHE’s extreme events team, said: “Cold does kill, even in places where the temperatures aren’t 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.”
Thursday marks the official start to winter with some forecasters warning this year could be a cold one.
Met Office forecaster Emma Sharples said the cold snap could last into next week thanks to high pressure wedged close to the UK.
She said: “High pressure will probably be in control of the weather until this time next week, temperatures will be lower under clear skies in the south than in the north where it will be cloudier.
“Later in the week the south and the southwest will still see widespread frosts while elsewhere they will be more patchy as cloud cover builds.
“Although temperatures will clim a little by the end of this week they will drop off again by the weekend.
“Tuesday night could beat Monday to be the coldest of autumn so far with Wednesday night looking like it will bring similar temperatures, maybe not quite as cold.”
If temperatures dip much below -7C (19.4F) overnight into Thursday it will be the coldest start to winter since they hit -15.3C (4.46F) in 2010.
The lowest overnight December 1 temperature since then was -7.2C (19.04F) at Livingston Mill, West Lothian, in 2012.
WeatherOnline forecaster Simon Keeling said: “A cool few days lie ahead as high pressure stays over or close to the UK and Ireland, overnight frosts and fog will occur too.
“It will be mostly dry although with increasing amounts of cloud, there are some indications of milder weather arriving towards the end of the forecast period, perhaps with some rain arriving in the west.”
Met Office experts blame environmental factors including a La Nina cooling of the eastern Pacific, weakening Polar winds and melting Arctic sea ice driven by warmer than usual North Atlantic waters for cold winter predictions.
Professor Adam Scaife, head of long-range prediction at the Met Office, said: “The stratosphere, tropics and Arctic sea ice are all trying to push our weather towards becoming colder over the next few weeks.
“Although it is not guaranteed, our long range predictions and those from other forecast centres suggest an increased risk of cold weather patterns early this winter.”