Freezing temperatures mean today is on track to be the coldest March day since 1986, forecasters said.
The unseasonably cold weather left travellers battling ice and snow, with the South of England being worst hit.
Jersey Airport was shut due to snow, and on the roads there were hazardous conditions on many major routes.
Blizzards were reported on the M40 in Warwickshire and there were numerous rush-hour accidents.
Strong winds added to drivers' problems with falling trees blocking some roads, while on the trains poor rail conditions led to delays in Sussex and Hampshire.
Forecasters warned of snow spreading to nearly every area of Britain, with almost 4in (10cm) expected in the worst-hit areas.
Although too early to officially record, it is thought to be the coldest at this time of year in 27 years.
The last time the UK experienced such a cold March day was on March 1 1986, Laura Caldwell, a forecaster with MeteoGroup, the weather division of the Press Association said.
In contrast, this time two years ago the country was basking in balmy temperatures of up to 17C (63F).
With more snow showers expected throughout the week, bookmakers have slashed the odds for a white Easter.
“Today has been a very cold day and it's going to be a bitterly cold night,” Ms Caldwell said.
“South-eastern England is seeing the worst of the weather along with the Channel Islands and should see two to 5cm of snow.
“Elsewhere, there will be scattered snow showers across much of the UK. It will be very frosty overnight but tomorrow will be a brighter day so will feel less bitterly cold.
“The South East of England will be the coldest overnight at minus 6 to minus 7C, and will remain the coldest tomorrow at around 2 to 3C. The warmest place will be the north-west of Scotland at 5 to 6C.
“It's not going to get warm any time soon.”
The closure of Jersey Airport meant a number of flights had to be cancelled.
Such severe blizzard conditions and strong gale force winds have not been seen on the island - normally regarded as one of the warmest parts of the country - in years.
It is feared the cold spell will have an impact on the main outdoor crop of Jersey Royals, which is planted from January to April.
On the roads, there were hazardous driving conditions on the A69 and A6 in Cumbria and on the A54 in Cheshire.
In Sussex, police said there had been “a number” of crashes caused by the snowy conditions as they warned motorists to take extra care on the roads.
While drivers contended with heavy snow on the M40 in Warwickshire, motorists in Wales had to put up with strong winds.
One lane of the M48 Severn Bridge was closed and falling trees blocked some Welsh roads.
Some of the roads where driving conditions were at their worst today included the A46 in Nottinghamshire, the A14 in Suffolk and the A353 in Dorset.
Fallen trees blocked roads in Newquay in Cornwall and in Lynton in Devon.
An RAC spokesman said it was on a red alert situation with its call centre teams and patrols dealing with 30% more breakdowns than on a normal Monday in March.
“By the end of the day we expect this to translate into the RAC helping 10,500 stranded members - 2,000 more than we had predicted for the time of year,” he added.
The bad weather meant no rail services were operating between Shanklin and Ryde Pier Head on the Isle of Wight, with minibuses running instead.
Condor Ferries services between Jersey and St Malo were also affected.
There was also a reduced service on TransEuropa Ferries' crossings between Ramsgate and Ostend, while services on Stena Line between Holyhead and Dublin were reduced.
Stena Line also had to cancel its 9am Rosslare to Fishguard service.
The cold snap led to the Local Government Association (LGA) putting out a warning to residents, postmen and milkmen to look out for elderly and vulnerable people.
Peter Box, chairman of the LGA's economy and transport board, said: “Council staff will be out and about over the next few days checking in on the people they know to be vulnerable and delivering hot meals and portable heaters, collecting prescriptions, defrosting pipes, fixing frozen boilers and making sure they have what they need.
“However, council staff can't be everywhere and we need support from our communities during prolonged freezing weather. We'd encourage anyone with elderly or vulnerable neighbours to call in on them over the next few days to make sure they're okay and not suffering in silence. Just a knock on the door of someone who's perhaps too proud or unable to ask for help can make all the difference.
“They may just need an extra blanket getting down from the loft or perhaps they didn't get out to collect their medicine this week. It takes very little time to check in on a neighbour but could potentially save lives.”