Commuters faced travel chaos on Monday morning as large parts of the UK were hit by ice, fog and snow following the coldest night of the year so far.
The Met Office issued yellow severe weather alerts due to the wintry conditions.
It was the coldest night of the year so far, with temperatures in northern Scotland dipping below minus 15C.
The Met Office said that the lowest temperature recorded was -15.6C at Braemer in Aberdeenshire, with the five next coldest temperatures all recorded in Scotland, including -13.1 at Balmoral.
Among the locations with fresh snow on Sunday was Andrewsfield, Essex (9cm), Charlwood, Surrey (5cm) and Herstmonceux, East Sussex (4cm).
Roads in eastern and south-east England are among the worst affected.
Drivers on northern sections of the M25 were stranded for several hours as traffic was at a standstill.
The UK’s busiest motorway was closed in both directions between Junction 23 for South Mimms and Junction 25 for Waltham Cross, in Hertfordshire, on Monday morning.
National Highways told road users at 8.15am: “The snow has been cleared, the road has been re-treated and all lanes are now open.”
They added that the closure was caused by “snow and jack-knifed lorries”.
Other roads in the area which suffered long delays included the M11, M2, A21, A27 and A249.
Sussex Police issued a warning for “treacherous” roads.
Daniel Duffield, a 22-year-old off-duty paramedic, was stuck on the M25 for more than two-and-a-half hours on Monday morning while attempting to travel home to Birmingham from London.
He told the PA news agency that vehicles have been “stationary with very small movement”.
He went on: “I expected some traffic due to weather but nothing this bad.
“Traffic appeared to be at a standstill for miles and miles.
“Other drivers were turning their engines off presumably to save fuel due to the uncertainty.
“A few people were stretching their legs due to delays too.”
He added that the road “doesn’t appear to have been gritted” but National Highways said “we had up to 25 gritters treating the M25 at any one time” on Sunday and overnight into Monday.
They spread a total of 960 tonnes of salt and more than 18,000 litres of anti-freeze.
It is essential to be prepared if you are driving— Edmund King, AA
AA president Edmund King said the number of breakdown callouts is around 25% higher than normal.
He went on: “Many drivers were stranded or severely delayed on the northern section of the M25 last night between London Colney and the M11.
“Traffic is still severely delayed there this morning due to the continuous snow fall.
“Roads in Kent were also severely affected including the M2, and M20.
“The conditions show that it is essential to be prepared if you are driving.”
He urged drivers to check fuel levels and take warm clothing, a charged mobile phone, food and drink.
“The best advice if you must drive is to take it easy and leave a much longer distance from the vehicle in front,” he added.
Several rail lines are closed, with Southeastern issuing a “do not travel” alert to passengers.
There is also major disruption to services run by Greater Anglia, South Western Railway and Southern.
There are minor and severe delays to London Underground trains, with all but the Waterloo & City line, Elizabeth line, and DLR affected.
Several parts of the network was suspended, including: the Northern line between High Barnet and Finchley Central.
Four children were taken to hospital in a critical condition after being rescued from a lake in Solihull in the West Midlands on Sunday afternoon after falling through ice.
Richard Stanton, area commander for West Midlands Fire and Rescue Service, said: “We know that the weather forecast for the next few days is expected to be bitterly cold, please, adults and children alike, stay away from open water, under no circumstances venture on to ice regardless how thick or safe you think this ice may be.”
More than 100 flights due to serve UK airports were cancelled across Sunday and Monday, with Gatwick, Stansted, Luton and London City airports among the worst affected.
An easyJet spokeswoman said: “Airlines operating to and from the UK today are experiencing some disruption to their flying programmes due to adverse weather, with a number of cancellations at Luton and Gatwick airports which are both affected by snow.
“Flights were also affected yesterday as snow closures affected Manchester, Liverpool, London Gatwick and London Luton airports with some flight cancellations and diversions.
“We are doing all possible to minimise the disruption for our customers, including providing hotel rooms and meals for those passengers affected by the cancellations.”
London City Airport said it is “experiencing some disruption this morning” due to aircraft being out of position after the “significant amount of cancellations” on Sunday night.
There is also a warning for wintry showers in many areas of northern Scotland and parts of north-east England for 48 hours from midday on Tuesday.
