Met Office forecaster Frank Saunders said: "Parts of England and Wales are likely to see their coldest spell of weather since at least 2013, and possibly since 1991."
Doctors have warned that the NHS could struggle to cope with the extra strain caused by the weather and are asking people to check on elderly or vulnerable neighbours during the cold spell.
Commuters were told to get home by 6pm and panic-buying shoppers were clearing supermarket shelves as the Siberian blast gripped the UK.
Shoppers have reportedly cleared some supermarkets shelves of bread and milk, while others have reported queues of over an hour, as desperate Brits panic-buy the basics.
A flurry of snow falls on a member of the Queen's Life Guard and his horse, guarding their ceremonial position outside Horse Guards during a sporadic snow shower in London. Photo / AP
Customers at a Tesco Extra branch in Gillingham, Kent, reported seeing chaotic scenes as people barged past each other to stock up.
Similar scenes were reported in Asda in Sittingbourne and Waitrose in Guernsey, where supplies of milk and bread have been snapped up by the public.
Snow showers will make the Tuesday morning rush hour tricky for some, with some disruption to travel likely. Aside from the #snow it is going to be a very cold start pic.twitter.com/mLUvkMFfqS
• Get home by 6pm or face being stranded as dozens of trains are cancelled and TfL Rail stops services.
• Check before they travel as trains and planes are hit by delays and cancellations with 50 BA flights scrapped at Heathrow.
• Stock up on medication and food in case roads and phone networks get cut off, particularly in rural areas.
• Brace for 18cm of snow for the next four days as Siberian wind sweeps UK - and Storm Emma hits from Wednesday.
Public Health England said the elderly and vulnerable are at "risk of death" as it urged people to take extra care in the unprecedented conditions.
ROME PARALYSED
The Arctic storm saw temperatures across much of Europe fall today to their lowest level this winter and even brought a rare snowstorm to Rome, paralysing the city and giving its residents the chance to ski, sled and build snowmen in its famous parks and piazzas.
Two women take a selfie in front of the Colosseum in Rome during a snowfall today. Photo / AP
Rome's schools were ordered closed, while train, plane and bus services were crippled. Italy's civil protection agency even mobilised the army to help clear slush-covered streets as a city used to mild winters was covered by a thick blanket of snow.
"Beautiful, beautiful!" marvelled Roman resident Ginevra Sciurpa, who donned a fur hat and thick scarf to brave the cold. "Even though I'm not a child any more, the enthusiasm for the snow is still the same. It is always beautiful, and above all I didn't have to go to work."
By noon the snow had all but melted, but freezing temperatures expected overnight prompted officials to close Rome schools todayfor a second day and warn of continuing traffic and train chaos due to the ice that was already forming on slick cobblestone sidewalks and streets.
Parks that usually stay green through winter were blanketed white, giving eager Romans a rare opportunity to go sledding, snow-shoeing or skiing. Even the Circo Massimo became a hot spot for snowball fights, while Piazza Navona, with its famed Bernini fountains, turned into a snow-dusted winter wonderland. Rome's Mediterranean climate and proximity to the sea usually result in mild winters, such that restaurants often keep outdoor seating open, albeit with space heaters, even through the coldest months of the year.
A street sweeper clears snow from a street in Stockholm as a wave of Siberian cold air sweeps across Europe and Scandinavia bringing extra low temperatures to the continent. Photo / AP
Elsewhere in Europe, the storm set dangerously low temperatures: Lithuanian officials said temperatures that plunged to as low as -24C in some places were to blame for the deaths of at least three people over the weekend.
Hospitals in Lithuania and Latvia have reported an uptick in people being treated for hypothermia and frostbite. Swedish Prime Minister Stefan Lofven's car skidded off the road in a snowstorm north of Stockholm and smashed into railing, one of several snow-related traffic accidents in Sweden. He was uninjured.
Meteorologists in Germany, meanwhile, reported a record low for this winter of -27C on the Zugspitze mountain in the Alps. Moscow, as well, recorded its coldest night this winter, with the mercury dipping to nearly -20C on Sunday night.
Doctors in Britain warned that the already-stretched National Health Service may have trouble coping with extra patients affected by what meteorologists are forecasting will be days of cold and high winds. British Airways cancelled a number of short-haul flights into and out of Heathrow Airport.
The intense winter weather has been dubbed "The Beast from the East" by British tabloids, citing the Siberian Arctic as the source of the frigid temperatures.
Sculptor Francesca Antonello moulds snow into a face as people look out towards the ancient Roman Forum covered in snow. Photo / AP
The storm system has moved progressively south and west and is expected to bring continued cold and snow for several days over much of Europe. In Croatia, about 1000 soldiers joined in the clearing operations in the worst-affected areas, where over 1.5m were reported. While unusual, the UN weather agency says such late winter cold spells aren't exceptional.
Scientists say the big chill in Europe is partly caused by the fact that strong winds which normally keep cold air "locked" over the Arctic have weakened, releasing icy blasts across the northern hemisphere. Similar sudden drops in temperature have occurred over North America in recent years and climate researchers say they could become more frequent as global warming further saps strength from the air currents around the pole.
Even as Europe shivers, temperatures in the Arctic itself have been unusually warm in recent weeks, the World Meteorological Organisation said. The Cape Morris Jesup station on Greenland's northern tip recorded temperatures above freezing several times since mid-February.
