A cold plume with a width of 1,000 miles will result in toxic air pollution and 10 days of fog and grey skies after a brilliant weekend of sunshine, according to forecasters.
Temperatures in the south of the UK are expected to plummet to -7C (19F) on Monday morning following a chilly Sunday morning of -6.2C in Oxfordshire and -6.8C in North Yorkshire.
But the coldest week since early December will see a cloak of grey for many as fog and low cloud trap air pollution due to high pressure and cold air.
The Met Office has warned that people's ears could pop on Monday when Britain experiences the highest atmospheric pressure in decades.
The predicted freezing temperatures has sparked a public health warning with the elderly and those with heart and lung problems being advised to stay indoors and heat their homes to 18C to fight off infections.
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Public Health England's weather alert is in place until Tuesday where cloud cover in central and southern areas will leave temperatures feeling particularly chilly.
A Met Office forecaster said: “After Monday's fog, frost and fog will plague the South from Tuesday to Thursday, with low cloud for the Midlands and North-West.
“Into the weekend stays cloudy for most. This will continue for the South further into the following week, while the North could be wetter and windier at times.”
MeteoGroup forecaster Mario Cuellar added: “Nights are the coldest of winter so far in the South, which had been almost frost-free, with -6C or so. Sunday night looks like the coldest.
"But fog, cloud and light winds will be like a blanket trapping pollution from power stations, cars and industry."
Issuing a pollution warning, DEFRA said: “Moderate air pollution is possible in parts, with a small risk of very high levels in the South-East. Light winds and fog patches allow the build-up of locally-emitted pollution.
Met Office 5-day forecast
Fog patches in the west could persist all day in a few places. Otherwise, mostly dry with sunny periods after a frosty start. The odd shower near coasts in the south-east, whilst cloudier and windier in the far north.
Tonight:
Frost and patchy fog in southern areas, whilst cloudier skies further north bringing some rain or drizzle to the far north and north-west, where it will also be windy.
Monday:
Dry with sunny spells in the south after frost and fog lifts. Cloudier in north-western parts with some rain in the far north, where it will be windy, but milder.
Outlook for Tuesday to Thursday:
Low cloud and patchy rain and drizzle will often affect central and northwestern areas; it will be bright at times in the northeast, while frost and fog plagues the south.