Two women died and another 47 people were injured after a coach overturned in treacherous icy conditions on one of the coldest nights of the year.
The vehicle, which was carrying 48 passengers and a driver back from a trip to see a Christmas lights attraction, left the road and ended up on its side last night near Penzance in Cornwall, Devon and Cornwall Police said.
It came as the poor Christmas weather continued for another day, with temperatures plunging as low as minus 10C (14F) in southern England and prompting widespread icy road warnings and more travel disruption.
Devon and Cornwall Police said road surfaces were "treacherous" in the area of the crash - which was near the town of Hayle - and have not ruled out the conditions as being a contributory factor.
A rescue helicopter was called in from RAF Chivenor in Devon to help ferry the wounded people to hospital in Truro.
One of two dead women - who were both from the west Cornwall area - was pronounced dead at the scene, while the other died in hospital.
Temperatures were said to have been minus 1C (30F) or lower in Cornwall, but far colder in other parts of the country already suffering from the wintry Christmas weather.
Middle Wallop in Hampshire - one of the worst-hit counties by this week's snowstorms - was one of England's coldest spots overnight at around minus 10C.
Temperatures in parts of London fell to minus 6C (21F), with Glasgow as low as minus 9C (16F), Cardiff minus 2C (28F) and the same temperature in Manchester.
Dalwhinnie in the central highlands looked to be one of the coldest spots this year, at minus 16C (3F) - just short of the minus 18C (0F) recorded at Aviemore in February.
As many as 12 million people are expected to travel to family and friends today and tomorrow, according to the AA, making it one of the busiest periods of the year.
The Met Office has issued several warnings of "widespread icy roads" for most of England, Scotland and Northern Ireland.
John Hutchinson, a forecaster with MeteoGroup, the weather division of the Press Association, said: "I think it will be the coldest night of the year for many places.
"There will be some patches of freezing fog that will be another hazard."
With predictions of patches of freezing fog as well, festive travellers face more disruption at airports and train stations as they try and getaway before Christmas Eve tomorrow.
Northern England and Scotland suffered the heaviest snowfalls overnight.
Passengers using Glasgow Airport were warned to expect delays and cancellations, with similar situations at Edinburgh and Aberdeen.
There were also warnings of disruption at Heathrow, Gatwick and Manchester - where staff have been working to clear heavy snow from the 750 acre site after a deluge yesterday.
Budget airline easyJet cancelled several dozen flights this morning, from airports including Gatwick, Stansted, Manchester and Luton.
A message on its website said: "We sincerely apologise for the disruption...but due to the current weather conditions, we have had to cancel some of our flights."
British Airways said the majority of its flights were operating normally.
But passengers were "strongly advised" to check their flight status before leaving for the airport.
Luton airport said today it was open, but warned some flights were subject to delay and cancellation.
Gatwick Airport also said it was open and the runway was operating as normal, but advised passengers again to contact their airline for the latest flight information.
Eurostar trains resumed a limited service yesterday after three days of suspension, clearing a backlog of passengers from the weekend.
A spokesman said it would continue to operate a restricted service today and on Christmas Eve.
Customers with tickets for travel between Saturday 19 and Thursday December 24 can come to the terminal either today or tomorrow.
There was disruption to train services yesterday in Scotland and elsewhere thanks to the snow falls and low temperatures, with operators battling to get services running normally last night.
The AA said it dealt with an estimated 18,000 breakdowns by the end of yesterday - compared with around 8,500 on a normal Tuesday. The figure compares with 22,000 on Monday.
AA president Edmund King accused some councils of not acting quickly enough to grit roads.
He said: "Councils should have acted sooner and more thoroughly.
"Some key roads have not been gritted at all. We've been inundated with calls from the public and our own patrols saying that yesterday, before the snow came down, there was little or no gritting."
The Local Government Association (LGA) said the claims aware "unverified, unsubstantiated and unjustified".