Heavy and “significant” snowfall threatens to grind parts of the country to a standstill before the end of this month, forecasters warn.
Numbing gales will send the mercury plummeting widely below freezing with fierce windchill making it feel close to -11C (12.2F) next week.
Cold weather will be driven by a rapid warming of air over the North Pole opening the floodgates to winds from the Russian Arctic.
A so-called Sudden Stratospheric Warming (SSW) threatens to keep Britain on ice into the start of spring on March 1.
The last major SSW event happened in January 2013 and was followed by one of the coldest Marches on record.
Temperatures began to rise over the North Pole in a similar pattern earlier this year sounding alarm bells to UK forecasters.
The mercury will nosedive from Tuesday after a mild and sunny weekend and start to this week.
Where breaks in the cloud allow sunshine across southern England tomorrow thermometers could touch 11C (51.8F).
However it will be a very different picture by the weekend with overnight lows of widely between freezing and -5C (23F), experts warn.
Met Office forecaster Marco Petagna said: “Temperatures will drop off through this week partly due to a cold front coming in from the northwest but also because we will start to see easterly winds develop.
“From this weekend there is the potential for very cold conditions to develop with harsh frosts and a risk of significant snowfall particularly to the east.
“Temperatures could feel much lower than they are because of windchill.
“The most likely situation is that cold easterly winds will continue to affect our weather through the end of the month and into March.
“There is always some uncertainty around SSW events as they don’t happen that often, but we expect to return to a colder regime certainly through the end of February and into the start of March.”
Met Office chief forecaster Frank Saunders added: “There is increasing confidence that the recent Sudden Stratospheric Warming above the North Pole could lead to prolonged cold conditions over the UK, increasing the risk of easterly wind and significant snow.”
“A Sudden Stratospheric Warming implies around a 70 per cent chance of cold conditions across the UK.
“Forecasts from computer models at the Met Office and at other centres are beginning to coalesce around a greater likelihood of cold conditions in the days and weeks to come.”
In 2013, the year of the last SSW, average March temperatures reached 2.2C (35.96F) across the UK, 3.3C below normal.
The next four years were milder apart from 2016 which brought an average March temperature of 5.3C (41.45F) – 0.2C below the norm.
Dr Peter Inness, a lecturer in meteorology at the University of Reading, said: “The last SSW event was in January 2013.
“What generally tends to happen is high pressure builds over Scandinavia bringing easterly winds along its southern flank.
“The air in this region is very cold at this time of year so when this happens it introduces colder conditions to the UK.
“Atlantic weather systems which are milder are blocked and we tend to see more of a flow from Scandinavia or even further east from Siberia.
“We think this will be a major warming event and as such will have a large impact on wind directions in the stratosphere bringing a change from westerly to easterly winds.”
The threat of a cold snap prompted bookies this weekend to take the axe to a raft of winter weather odds.
Coral is offering 6-4 on the coldest February on record with evens on 2018 being the coldest year ever.
Spokesman John Hill said: “The glorious sunshine is not expected to last very long before the cold snap returns again.”
Ladbrokes is offering 4-6 on the coldest day of the year so far being recorded this week with 1-3 on snow in London.
Spokesman Alex Apati said: “The cold, wet and windy weather looks set to stay put for the next two weeks as February 2018 looks set to break a whole host of records.”
Exacta Weather forecaster James Madden warned the next cold snap could bring the heaviest snowfall of winter so far.
He said: “Despite a mild start to Monday it will turn significantly colder for the rest of the week from Tuesday onwards as winds veer in from a much colder easterly direction.
“A small nudge downwards in temperatures could see this month challenging the coldest February on record.
“Snow is likely to return during the final third of this month and into the early part of March to start the meteorological spring proper, this is likely to cause widespread disruption.
“Current forecasts indicate we could be facing the most significant snowfall of winter so far.”