Britain shivered through the coldest night of the winter so far as temperatures plunged lower than minus 12C last night and the country braced itself for up to 15cm of snow.

Parts of the UK were placed on amber alert, the Met Office's second highest severe weather warning, as flights were cancelled and a string of sporting fixtures fell victim to the big chill.

On the roads, motorists faced a "dangerous cocktail of driving conditions" while forecasters warned the freezing weather was set to stay.

The cold snap has already seen daytime temperatures plummet four or five degrees lower than average for February - traditionally the chilliest month of the year.

The mercury dropped to minus 12.4C in South Newington, Oxfordshire, last night - the lowest recorded temperature this season, the Met Office said.

Most parts of the country are expected to wake up to a blanket of snow tomorrow morning, with up to 15cm forecast in some places, including London's Heathrow Airport, where a third of flights will be grounded amid adverse weather conditions and the possibility of freezing fog.

Met Office forecaster Michael Lawrence said: "We have got a band of rain, sleet and snow pushing in from western parts.

"This is running over colder air and that's going to give some fairly significant snowfall, mainly in eastern and central parts of Britain and - to some extent - large parts of the UK."

While some regions - including Cumbria, Lincolnshire, East Anglia, North Yorkshire, the Peak District and the Midlands - are expected to see a 15cm dumping of snow, many regions will get between 5cm and 10cm.

Wales and the South West, along with parts of western Scotland, will mostly see rain.

The amber alert in England applies to Yorkshire and Humber, the West Midlands, East Midlands, the East, the South West, London, the South East and the North West.

A yellow alert, which warns people to "be aware", was in place for parts of Scotland, Wales and north-west England.

Much of England is also under a cold weather alert of level 3, which warns of "100% probability" of severe cold weather, icy conditions and heavy snow.

Temperatures are forecast to stay around zero today, occasionally dropping below freezing, while London is likely to experience highs of 3C.

The deep freeze, which is likely to continue into next week, is expected to cause treacherous conditions on the roads.

The RAC said the situation was likely to deteriorate this afternoon and urged drivers to stay at home where possible.

Kevin Andrews, RAC patrol ambassador, said: "It looks like we're going to get a dangerous cocktail of driving conditions this weekend, with heavy snow and sub-zero temperatures making the roads extremely treacherous."

The motoring organisation said it was attending 70% more breakdowns than normal while a spokesman for the AA said it had been called out to deal with more than 4,300 vehicles this morning - around 1,500 every hour.

This figure is predicted to reach up to 16,000 by the end of the day, almost double the 8,500 of a usual Saturday.

The Local Government Association (LGA) said an army of council staff and volunteers would be braving the elements to make sure vulnerable people were cared for.

"Thousands of new grit bins have been placed in estates and side streets, residents have been given their own bags of salt along with salt spreaders in some neighbourhoods, and arrangements have been made with parish councils, community groups, snow wardens and farmers to grit hard-to-reach areas," a spokesman said.

British Gas said its fleet of all-weather 4x4s was on standby to get engineers out to customers and keep Britain warm during the cold snap.

A spokesman said the company had received more than 200,000 calls in the last five days, compared with 120,000 to 140,000 during a normal winter week, and was expecting a further 50,000 this weekend, compared with 20,000 normally in the winter.

The Department for Transport has said it was better prepared than ever for severe winter weather.

Salt stocks across Britain stand at more than 2.4 million tonnes - a million more than last year.

But they were of little comfort to sports fans hoping to see Portsmouth's home match against Hull City which became the first Championship fixture cancelled due to a frozen pitch.

Several matches in the lower leagues have also been called off while racing was also heavily hit.

But swimmers were not deterred by ice on the Serpentine in London's Hyde Park this morning and gritted their teeth as they plunged into its chilly waters.