Last December was the warmest since records began in 1910 – but the UK's run of mild winters could be about to end.

An icy polar vortex could descend from the Arctic in the coming months and cause temperatures to plummet, the Met Office has warned.

There is an "increased risk of cold snaps between now and Christmas,” the forecaster said in a recent blog post.

Several factors could make the possibility of a cold start to winter more likely, from tropical rainfall conditions to disruption to air flow over the equator, it said.

But there is a higher chance this year that "weak stratospheric circulation" caused by a polar vortex could bring icy winds and freezing weather to the country.

What is a polar vortex?

A polar vortex is a mass of very cold air which sits above the Earth’s north and south poles.

This dense, cold air is controlled by a large pocket of low pressure, which rotates in an anti-clockwise direction at the north pole and clockwise at the south pole.

A pedestrian makes their way along a snow packed street in Indianapolis (Michael Conroy/AP)

Why does it move south from the poles?

The strength of a polar vortex varies from year to year. When it is strong, the vortex is concentrated over the Arctic or Antarctic area.

But when it is weak – which is more frequent – it can split into two or more freezing vortices.

These cover a larger area and can move south to Canada, the USA and Europe, increasing the risk of air temperatures decreasing to potentially dangerous levels.

Timelapse shows mist clearing from the London skyline

When is it coming to the UK?

The polar vortex in the northern hemisphere is weaker than usual this year.

“There’s a higher chance of cold being able to sink southwards, whereas if it was fast, it would stay on its normal track around the poles,” Met Office forecaster Emma Sharples told The Independent.

Although polar vortex winds are many kilometers above the ground, they can “influence the strength and position of the jet stream,” according to the Met Office. “This is helping to increase the risk of cold snaps in the UK.”

Ms Sharples said the arrival of a polar vortex could help the jet stream become “more north-south orientated rather than west-east like last winter."

“When there are more kinks in [the jet stream], that means more areas of cold air coming south across the UK,” she said. “But that’s only one thing of many that can affect what kind of weather we can have”.

When is the last time this happened?

A polar vortex made headlines in 2014 when much of the United States was hit by an extended period of cold weather, causing transport chaos and bringing some parts of the country to a halt.

The weather conditions sparked by the vortex were so severe that even the polar bears at Lincoln Park zoo in Chicago had to be brought inside.

In pictures: 'Polar vortex' hits US Midwest and Northeast Show all 30 1 /30 In pictures: 'Polar vortex' hits US Midwest and Northeast In pictures: 'Polar vortex' hits US Midwest and Northeast USA An AAA emergency technician assists a motorist on Bidwell Avenue in Buffalo, New York In pictures: 'Polar vortex' hits US Midwest and Northeast USA Ice forms on the shore of the East River due to unusually low temperatures caused by a Polar Vortex in New York In pictures: 'Polar vortex' hits US Midwest and Northeast USA A man braves the cold and walks along the shore of Lake Michigan as temperatures remain in the negative digits in Milwaukee, Wisconsin. A 'polar vortex' of frigid air centered on the North Pole dropped temperatures to the negative double digits at its worst In pictures: 'Polar vortex' hits US Midwest and Northeast USA Snow is piled high along the street outside the front of a home in Indianapolis, Indiana. A deadly blast of arctic air shattered decades-old temperature records as it enveloped the eastern United States, canceling thousands of flights, driving energy prices higher and overwhelming shelters for homeless people In pictures: 'Polar vortex' hits US Midwest and Northeast USA Jennifer Berry watches the sunset from a lifeguard chair at a beach on Lake Calhoun in Minneapolis. Shortly after daybreak in the Twin Cities, thermometers had inched their way up to anywhere from 8 to 13 below zero In pictures: 'Polar vortex' hits US Midwest and Northeast USA Ice builds up along Lake Michigan at North Avenue Beach in Chicago, Illinois In pictures: 'Polar vortex' hits US Midwest and Northeast USA Chicago hit a record low of -16 degree Fahrenheit this morning as a polar air mass brought the coldest temperatures in about two decades into the city In pictures: 'Polar vortex' hits US Midwest and Northeast USA Ice builds up along Lake Michigan as temperatures dipped well below zero in Chicago, Illinois In pictures: 'Polar vortex' hits US Midwest and Northeast USA Clouds of steam rise from the Mississippi river during -14 Degrees Fahrenheit (-25 degrees Celsius) weather, in Minneapolis, Minnesota In pictures: 'Polar vortex' hits US Midwest and Northeast USA A view of the War Memorial in Indianapolis, Indiana. According to news reports, Indianapolis received about 30 centimeters of snow and the morning temperature was -9 degrees Celsius In pictures: 'Polar vortex' hits US Midwest and Northeast USA A horse drinks water from a hole in a frozen water tank in Enid, Oklahoma. Record low temperatures were set in at least two Oklahoma cities as a frigid front moved into the state In pictures: 'Polar vortex' hits US Midwest and Northeast USA Ron, a bison at Brookfield Zoo, is covered in snow and doesn't seemed phased by the frigid temperatures or snow blowing through the Chicago area. The zoo was closed due to the snowstorm and sub-zero temperatures In pictures: 'Polar vortex' hits US Midwest and Northeast USA A woman walks through a gust of blowing snow in frigid cold temperatures though downtown Chicago, Illinois. A blast of Arctic air gripped the mid-section of the United States, bringing the coldest temperatures in two decades In pictures: 'Polar vortex' hits US Midwest and Northeast USA Washburn High School's information board reads -14 Degrees Fahrenheit (-25 degrees Celsius), in Minneapolis, Minnesota. Schools in the area were closed due to the severe weather In pictures: 'Polar vortex' hits US Midwest and Northeast USA Patrick O'Brien dressed up in a Spiderman superhero outfit goes for a run in -25 degrees Celsius weather, in Minneapolis, Minnesota In pictures: 'Polar vortex' hits US Midwest and Northeast USA Snow is piled up high in front of Home Depot in the South Bay shopping center after a two day winter storm in Boston, Massachusetts In pictures: 'Polar vortex' hits US Midwest and Northeast USA A man wears a face mask and heavy clothes while walking through downtown Springfield, in blowing and falling snow as a strong winter storm moves through the Midwest. Temperatures not seen in years are likely to set records in the coming days across the Midwest, Northeast and South, creating dangerous travel conditions and prompting church and school closures In pictures: 'Polar vortex' hits US Midwest and Northeast USA A city snow plow clears a street of snow in an almost deserted downtown as strong winds and snow move through the Midwest in Springfield In pictures: 'Polar vortex' hits US Midwest and Northeast USA A man prepares to remove his plow stuck in a snow bank as snow and wind swirls in St. Louis In pictures: 'Polar vortex' hits US Midwest and Northeast USA A Delta airlines plane is seen taking off while the fleets other planes sit on the tarmac at JFK Airport, New York In pictures: 'Polar vortex' hits US Midwest and Northeast USA Four homeless men warm themselves on a steam grate by the Federal Trade Commission, blocks from the Capitol, during frigid temperatures in Washington. A winter storm that swept across the Midwest this week blew through the Northeast, leaving bone-chilling cold in its wake In pictures: 'Polar vortex' hits US Midwest and Northeast USA Nicholas Simmons warms himself on a steam grate with three homeless men by the Federal Trade Commission, just blocks from the Capitol, during frigid temperatures in Washington In pictures: 'Polar vortex' hits US Midwest and Northeast USA New York City Department of Parks & Recreation employees clear out snow from Carl Schurz Park after an overnight storm dropped up to 7 inches of snow in New York City. The Northeast and Midwest regions of the United States were hit with a large amount of snowfall accompanied by blizzard-like winds and plummeting temperatures this week In pictures: 'Polar vortex' hits US Midwest and Northeast USA A man falls while slipping on ice during freezing rain on Roosevelt Island, a borough of Manhattan in New York In pictures: 'Polar vortex' hits US Midwest and Northeast USA A couple walks through the winter white-out on Swan Avenue in Webster Groves In pictures: 'Polar vortex' hits US Midwest and Northeast USA Few cars drive on Interstate 44 in Fenton. Snow-covered roads and high winds were creating dangerous driving conditions from Missouri to Delaware ahead of a 'polar vortex' that'll bring below-zero temperatures not seen in years to much of the nation in the coming days In pictures: 'Polar vortex' hits US Midwest and Northeast USA People carry bundles of warm weather wraps as they arrive outside Lambeau Field before the start of the NFL Wild Card playoff game between the San Francisco 49ers and the Green Bay Packers in Green Bay, Wisconsin In pictures: 'Polar vortex' hits US Midwest and Northeast USA Joe (R) and Rick (L) Pecki wait for the gates to open outside Lambeau Field before the start of the NFL Wild Card playoff game between the San Francisco 49ers and the Green Bay Packers in Green Bay, Wisconsin. Temperatures are around 5 degrees (-15 C) and are expected to go lower throughout the next few days In pictures: 'Polar vortex' hits US Midwest and Northeast USA An icy tennis ball was no deterrent for Laura Jorgensen's dog Wilber while they played in a dog park in sub-zero weather as the midwest braces for the coldest temperatures in nearly twenty years to arrive in later today in Minneapolis, Minnesota In pictures: 'Polar vortex' hits US Midwest and Northeast USA James Schlafer and his wife Diana Schlafer of Minneapolis went for their daily four to five mile walk in sub-zero temps as the midwest braces for the coldest temperatures in nearly twenty years to arrive in later today in Minneapolis, Minnesota

In the UK, extreme conditions were experienced in the winter of 2010, when the normal pattern of Arctic winds broke down causing a weakened polar vortex to allow a frigid body of air to move south.

This brought record snow conditions to northern Europe, eastern Asia and eastern North America.

How long could the cold spell last?

Met Office scientist Jeff Knight told The Independent the polar vortex effect on the UK's atmosphere tends to affect the weather "with a few weeks' lag".

Dr Knight emphasised that the vortex was an "external factor" that could influence the weather, rather than being "intimitely linked" with weather conditions.

"You can view the weather as rolling a dice. But something like a weak stratosphere is like loading the dice," he said.

"Because it’s weak, there’s a higher chance we’ll see colder weather with less of the Atlantic storms that bring moisture and warmth to these shores."

He said the weak polar vortex could affect the whole North Atlantic region, meaning the risk of cold snaps is greater for North America as well as Europe.

"It’s important to say that it’s only an increased risk," he said. "There’s still a good chance we’ll have an ordinary winter. We don’t tend to get cold and snowy winters often in the UK, but it’s slightly more likely than usual."

What are the risks?

According to the Office for National Statistics, there were nearly 44,000 extra winter deaths in 2014-15. A particularly cold winter puts elderly and vulnerable people at risk.