Ice warnings are in place for much of the country after more than four inches (10cm) of snow settled in some places.Sleet and snow began falling in central, eastern and southern areas overnight with most areas from Scotland down through to southeast England hit with a covering of at least two inches (5cm).
And the worst affected areas, including north England and the Midlands, could have twice that.
More than four inches has already settled in High Wycombe, Buckinghamshire.
The snow is expected to stop later this morning, but the accumulations could still cause travel disruption.
The Met Office has issued yellow weather warnings affecting much of England, Scotland and Wales, because of the danger of ice following the snow.
More light flurries are predicted for today and tomorrow, after which the week is expected to turn milder.
Sky News meteorologist Chris England said: "Eastern Wales and central and eastern parts of Scotland and England will see widespread snow overnight. The snow will clear from Scotland and northern England later.
"Elsewhere, western Wales, southwest England and Ireland will mostly have rain, but there will be some snow too, mainly over the hills. It will turn mostly dry there by morning.
"Today will be rather dull for southern Britain and Ireland, with a little rain in the west and a few snow flurries in the east, but southwest England will enjoy bright spells.
"Scotland and northern England will be mainly dry with some sunshine, once wintry showers clear the far north. It will be cold in the north and east, with a rather chilly breeze.
"Tuesday will be cold and dry for most, but Ireland will see rain moving into the west later. That rain will spread to Britain on Wednesday, bringing more snow to the north."
Meanwhile, thousands of UK passengers have been stranded in the US after flights to Britain were grounded when a massive snowstorm hit the US east coast.
It dumped more than three feet of snow from Massachusetts to New Jersey, while hurricane-force winds battered the eastern states and up into Canada, killing at least eight people.
Heathrow Airport said 10 inbound flights - all from New York and Boston - were cancelled today, as was one outbound flight to Washington.
British Airways, Virgin Atlantic, Delta Air Lines, United Airlines and Air Canada were all forced to cancel flights, Heathrow said.
Passengers were advised to check if their flights are affected with their airlines.