It’s time to get out the thermal underwear and thickest pullovers – Britain is set for shockingly cold weather for at least the next couple of weeks.

After a glorious Christmas, with not a hint of a snowflake, temperatures have been slipping steadily downwards, with minus 11C (12F) recorded in Aviemore, in the Highlands, on Saturday night.

The plunge into a Siberian blast of cold will worsen in the coming week as raw easterlies freeze the country. “This coming week, maximum daytime temperatures will be between 2C (36F) and 4C (39F) but temperatures at night could be well below zero for many places,” said Stephen Holman, forecaster at the Met Office.

The freezing conditions are being swept down from a strong high-pressure system anchored close to Scandinavia. Like a boulder firmly stuck in a river, this anticyclone is refusing to budge and sending our usual wet and windy winter weather on a wide detour, a system known as a blocking weather pattern.

Although it will feel bitterly cold, conditions will also largely be dry, at least for the next few days, and no significant snowfall is expected, although northern and eastern regions could experience some snow.

Exactly how cold it will become largely depends on where the high pressure sits and how much cloud it drags off the North Sea. And cloudy skies are needed, because they act like a duvet cover, helping to prevent some of the heat loss from the ground. If the nights turn clear and winds are light, though, temperatures could plummet as low as minus 10C (14F) even in the South of England in the next fortnight.

In winter, low pressure tends to dominate over Iceland and high pressure to the south, over the Azores. These two pressure systems dance in tune with each other and drive our winter weather, in what is known as the North Atlantic Oscillation (NAO). When the Icelandic low and Azores high are strong, they steer wet and mild weather over the UK; but when they slacken off in a negative phase, that turns the UK bitterly cold. At present the NAO is turning negative, sending a powerful signal that the weather is set to continue cold.

How bad could this winter sink? The weather maps are a chilling reminder of some our most savage winters, such as the notorious 1962-63 winter, the coldest for 180 years. This was when the sea froze around the coast of southeast England and crops were dug out of frozen ground with pneumatic drills and blizzards paralysed the nation.

Even if next month is freezing, the Met’s long-range forecast predicts that the winter will melt away into warmer conditions in February.

— Fears are growing for the safety of a 21-year-old man from South Uist, in the Outer Hebrides, who disappeared after attending a Christmas dance. Police, coastguard teams and hundreds of volunteers have been looking for Simon Macmillan, who has not been seen since 3am on Friday, when he got off a minibus in the Linique area of Iochdar, a few miles from his home. Temperatures fell below zero at the weekend.

Winter Tales

— The winter of 1647-48 was probably the coldest since daily temperature records began to be kept in the 17th century. John Evelyn, the diarist, records a journey by coach and horses from the City of London to Lambeth along the frozen Thames

— In London, where the most extensive records were kept, snow fell for 39 consecutive days in the winter of 1739-40

— Much of Britain was under snow from December to March, 1962-63

— In February 1947 snow fell on the British Isles on all but two days of the month, with more snow and gales in March, and drifts 3m (9ft) deep in the Chilterns

— Severe flooding followed the thaw of 1947 as the frozen ground was unable to absorb the water