Motorists have been urged to take extra care in treacherous conditions as snow across much of the UK turns to ice.
The Met Office has issued nine warnings for ice after disruption to road, rail and air travel following up to 16cm (6in) of snow in some areas.
Half of the 1,300 scheduled flights at Heathrow were cancelled and some trains and Tube services also disrupted.
Almost 400 transatlantic passengers are stranded overnight in Ireland after six London-bound flights were diverted.
Earlier, hundreds of vehicles were stranded on the M25 and M40, with some drivers forced to spend the night in their cars.
Snow swept down to London and East Anglia on Saturday evening after covering parts of Scotland, Wales, northern England and the Midlands earlier in the day.
Church Fenton, in North Yorkshire, reported 16cm (6in), which contributed to more than 60 accidents on the region's roads.
BBC forecaster Holly Green said ice was likely to be a hazard, particularly across much of England and south-eastern parts of Wales, as rain hits frozen surfaces and lying snow freezes overnight.
She said there was a risk of further small accumulations of snow in eastern parts of England on Monday morning, with patchy rain elsewhere.
The Met Office advised people to "be aware" of the dangers of the icy conditions.
In other developments:
- Forecasters warned of widespread ice in Wales as the worst of the weather eased
- A 55-year-old man was airlifted to hospital after injuring his spine in a sledging accident in Terrington, North Yorkshire
- A 35-year-old woman was taken to hospital with hypothermia after being rescued from a frozen lake in Beeston, Nottinghamshire, on Saturday evening
- London Ambulance Service experienced a surge in 999 calls with 2,500 in the 12 hours to midday - up 26% on the same period last Sunday
- Key roads in and out of Dover were closed after heavy overnight snow in Kent, while rail operators reported delays and cancellations
- There were several incidents in Surrey overnight, including a car that ran into the back of ambulance in Ashford
- In Staffordshire more than 100 vehicles were abandoned on the A50 in Uttoxeter after two lorries jack-knifed, although the road has been re-opened
- There were warnings of icy roads after 5cm of snow fell in parts of Scotland
- Sunday's Championship match between Derby County and Nottingham Forest was postponed and all three horse racing meetings in the UK - Fontwell, Kempton and Musselburgh - cancelled
Two British Airways flights from Atlanta, carrying 122 passengers, and Dallas, with 259 onboard, which were due at Heathrow, remain grounded at Shannon Airport in Ireland.
They were among six flights forced to land at the airport in County Clare because of the cold conditions. They are expected to depart for London on Monday morning.
Heathrow operator BAA said it had decided to reduce the flight schedule at Heathrow on Saturday to "minimise disruption" and said airlines had been able to re-book some passengers as a result.
Richard Scott, from BAA, said because Heathrow operated at capacity, there was no slack in the system to deal with the reduced number of flights that could take off and land in bad weather.
He added: "If we don't proactively cancel flights, the delays build and build and build and it's much worse for passengers."
Transport Secretary Justine Greening said she supported the "resilience plan" between the airport and air traffic control.
"It was a co-ordinated effort and a decision they took to cancel flights in advance so we didn't have passengers turning up at the airport and then finding their flight was cancelled," she said.
"So I think that was actually the right approach to take."
Shadow foreign secretary Douglas Alexander said it seemed a sensible precaution.
At Stansted Airport in Essex, flights were operating but queues in the terminals were busier than normal as schedules were disrupted.
A dozen Ryanair flights were cancelled, some planes were delayed whilst de-icing took place, and there was a knock-on effect from 11 inbound flights being diverted away on Saturday night during snow clearing.
At Gatwick, flight arrivals and departures were operating, although passengers were warned they may face some disruption.
At Luton Airport, 10cm of snow fell overnight and its runway was closed for a period, causing three departing flights to be cancelled.
Passengers were warned that flight departures and arrivals may be subject to delay or cancellation.
British Airways said it would allow passengers scheduled to fly on Sunday to re-book for journeys between Monday and Thursday.
Birmingham Airport reopened after closing whilst snow was cleared from the runway, and Leeds Bradford Airport has warned of delays or cancellations.
On the roads, Thames Valley Police said as many as 100 vehicles were stationary on the M40 between Junction 4 High Wycombe and Junction 9 Bicester for several hours and snow ploughs were brought in to help clear the roads.
Motorist Katie Jones told BBC News she had spent hours sitting in her car on the M25 in Hertfordshire.
"We were stationary for about seven and a half hours. We passed cars abandoned in the side of the road, having crashed off. We passed lorries jack knifed across two, three lanes of the motorway and it's been impassable in large part."
Transport for London said several Tube lines were hit by suspensions or delays. earlier on Sunday.