Temperatures recorded in England and Wales were the lowest in those countries this year as fresh snow fell in places overnight.
The mercury fell to minus 9.9C in Shap, Cumbria, overnight and minus 7.6C in Sennybridge, on the northern edge of the Brecon Beacons, as many woke up to the coldest morning of the week, the Met Office said.
But the coldest temperature overnight was recorded in Tulloch Bridge, in the Scottish Highlands, where the mercury plunged to minus 10.1C - still some way off the UK's coldest night of 2018 so far at minus 13.7C.
Yellow weather warnings for snow and ice were in place on Wednesday morning for the South East and western areas of England, Wales and Scotland, as well as all of Northern Ireland.
Emergency services warned of treacherous conditions on roads, with South Western Ambulance Service reporting several accidents due to ice and Northumbria Police attending a three-car crash in Gateshead, where the roads were "extremely icy".
Met Office meteorologist Martin Bowles said there was some snow fall in the south-east of England, which settled in areas including Norfolk.
There were also snowy scenes in parts of Kent, including West Malling and Tunbridge Wells.
Mr Bowles said the snow showers would ease off and most areas of the UK would see a dry sunny but cold day.
He said: "For much of the country, a big chunk of England and Wales and southern Scotland is going to be dry and colder, with temperatures below average still."
Heading into Wednesday night, a band of rain and snow will spread south-east towards the north west of England, Northern Ireland and later on into Cornwall and Devon, he said.
"It will mainly be milder than the night before, however in the far south east, there will be colder temperatures than we had last night," Mr Bowles said.
"We could see minus 4C in London."
Earlier, the Met Office tweeted: "For many Wednesday morning will be the coldest of the week, with a hard #frost, #ice and some #snow. Scrapers at the ready!
"Snow showers in the southeast easing through afternoon. A few wintry showers possible in west Wales and Cornwall. Cloudier across Scotland and Northern Ireland with rain, sleet and snow edging southeastwards."