Snow has fallen across much of the UK overnight, with forecasters warning that there is likely to be more later.
Overnight snow descended in north-east England, Manchester and north Wales and headed down towards the Midlands, with similar conditions in southern England.
With wintry conditions in Wales, Scotland and Northern Ireland, the Met Office has issued a number of flash warnings of severe or extreme weather.
BBC Weather warned driving would be "treacherous" in many areas.
Snow also fell in London, causing flight cancellations and delays across the UK.
British Airways said 62 flights had been cancelled at Heathrow airport's Terminal 5.
Birmingham International has taken some flights that were diverted away from Heathrow.
There were cancellations at Gatwick and passengers at Bristol International Airport have experienced delays.
A BBA spokeswoman said: "Our advice to passengers using any BAA airport is to check the status of flights with your airline or tour operator, before travelling to the airport."
Up to 8cm (3in) of snow is likely to fall in parts of southern England on Sunday, according to BBC weather forecaster Chris Fawkes.
But the snow was expected to clear in this part of the country later.
Wales, Scotland and Northern Ireland have experienced wintry conditions.
And the forecaster said more heavy snow was expected in northern England, west Wales and south west England.
He forecasted intermittent snow showers, between spells of sunshine, in Northern Ireland and Scotland.
Mr Fawkes said temperatures in large towns and cities are set to fall to as low as -2C.
"This makes it a very cold day for April. It follows on from the warmest day of the year so far on Thursday, in Inverbervie, Aberdeenshire, where the temperature was 18.9C," he said.
The forecaster added that there was the possibility of further snow showers in some parts of the UK on Monday.
The M56 between junctions 10 and 11 near Warrington has been closed in both directions because of sheet ice, which has led to a number of collisions - although none were understood to be serious.
A Cheshire Police spokesman said: "We would ask all motorists to avoid the area and seek alternative routes across the county.
"We are unsure at this stage how long that closure will be in place."
And there have been accidents on the M40.
A Thames Valley Police spokesman said Bicester, Aylesbury and Oxfordshire had all seen heavy snowfall, with several reports of cars struggling to continue their journeys and minor accidents.
Snow in Scotland and parts of northern England on Saturday hampered the search for a missing aircraft in the Highlands.
The light aircraft disappeared off radar as it was crossing the Cairngorms, south east of Glenmore Forest, in poor weather on Saturday morning.
Temperatures have dropped significantly over the weekend after a warm week that had included the hottest day of the year on Thursday.
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