Temperatures dropped below -6C overnight as parts of the country remain under a cold weather health alert.
The Met Office said it got down to -6.6c in Sennybridge, Powys, while Shap in Cumbria and Eskdalemuir in Dumfries and Galloway had -6.5C.
It meant it was "the coldest night of the season so far", the Met Office added.
It was slightly warmer in Northern Ireland, where Katesbridge in County Down fell to -3.8C.
Friday morning brought the first widespread frost of autumn for many, and much of the UK will today be sunny but chilly under clear blue skies - a far cry from the thick fog at the start of the week.
The Met Office's chief forecaster, Chris Bulmer, said the UK had "moved to a colder phase" and most places would be stuck in single digits ahead of another cold night.
"Overnight temperatures on Friday night will dip again to -4 or even -6C in some locations, meaning another significant ground frost for many locations" said Mr Bulmer.
Get the Sky News Weather forecast for your area
A cold weather health alert - the first of the season - is in force in the northwest of England and the West Midlands until noon on Saturday.
The yellow warning, issued by the UK Health Security Agency, warns of an increased risk to over-65s and people with certain health conditions.
"It is vital to check in on friends, family and neighbours who are most vulnerable," said UKHSA consultant Dr Anya Gopfert.
The Met Office is forecasting an unsettled outlook over the next few days.
It said heavier rain and showers will move in from the west, which could mean spells of sleet - and even some snow.
But most of us won't need to dust off the wellies just yet: as is often the case, it's expected to be confined to northern Scotland.
Around 2-5cm could accumulate in areas above 400m, but there could be "temporary accumulations" as low as 200m.
(c) Sky News 2026: UK weather: Temperatures drop to -6C with cold weather alert in force in some areas
'Face' of mystery woman found dead in bin bag in Liverpool park released by police
Former Hamas bodyguard unmasked after 'plotting terror attack' when given British citizenship
Jeffrey Donaldson's wife Eleanor placed on sex offenders' register after his rape conviction
Mauricio Pochettino breaks down in tears during press conference
Two Iranians convicted of spying for their country after entering Britain illegally
Mechanic offered 'special serum' to man who drugged and raped wife, court hears
