Freezing fog played havoc with travel on Wednesday, with flights cancelled, roads jammed and delays on main line rail and Tube services.
The worst of the fog had lifted by evening, with Heathrow having earlier cancelled around 60-70 flights.
London City Airport also had to axe six early-morning flights, as UK temperatures dipped as low as minus 10C (14F).
Cancelled flights at Heathrow included scheduled trips to Warsaw, Nice, Stockholm, Aberdeen and several German cities.
There was congestion on a number of major roads, while a section of the A1(M) between junctions 39 and 40 in Yorkshire was closed.
On the railways, overhead wire problems caused 50-minute delays in the rush-hour between Bedford and Luton, while a broken-down train at Watford Junction in Hertfordshire also caused hold-ups.
An electrical supply problem led to delays to train services between Seaford and Lewes in East Sussex, while a signalling problem caused hold-ups to services in and out of another Sussex coastal station - Brighton.
In Scotland, a broken-down train at Bathgate led to delays between Edinburgh and Airdrie.
On the Tube, there were severe delays on the Metropolitan line between Rickmansworth and Amersham and minor delays on the rest of the line due to a lack of trains.
There were also severe delays between High Barnet and Finchley Central on the Northern line due to a signal failure at Woodside Park.
Another signal failure - at Arnos Grove in north London - led to delays on the Tube's Piccadilly line between Arnos Grove and Cockfosters.
The coldest spot in the UK on Tuesday night was Tulloch Bridge in the Highlands, where the thermometer could only creep up to minus 10.2C (13.6F).
Other overnight cold spots included Chesham in Buckinghamshire at minus 9C (15.8F) and Little Rissington in Gloucestershire where it was minus 8C (18F).
"The fog is not as extensive as it was this morning - a lot of has lifted," said Bill Payne, a forecaster with MeteoGroup, the weather division of the Press Association.
"It's going to be another cold night with widespread sharp frost again with temperatures reaching the minus five mark."
Overhead wire problems between Northampton and Rugby led to buses replacing trains between Northampton and Coventry, while an hourly train shuttle was running between Coventry and Birmingham New Street, with journey times in the area extended by up to 60 minutes.
There were also overhead wire problems affecting services in and out of London's King's Cross station.
The bad weather disrupted services at Christ's Hospital in Sussex, with trains between Barnham and Horsham delayed.
A broken-down train at Melton Mowbray in Leicestershire led to delays of up to 45 minutes between Leicester and Peterborough.
Police closed a three-mile stretch of the A24 southbound in the Horsham area of West Sussex after "treacherous" black ice caused 12 vehicles to skid and crash.
Nobody was seriously hurt but a few drivers suffered minor injuries and damage to their cars, Sussex Police said.
In Dorset, motorists were urged to take extra care after a gritting lorry overturned on ice early this morning.
The accident on the B3351 Studland Road near Purbeck Golf Course at about 2.15am caused the lorry to shed its load of salt and grit across the carriageway.
Dorset Police said the road was closed both ways with a diversion in place to allow the gritter and its load to be cleared.
A police spokesman said there had been no reports of any injuries.
For chilly images, see the gallery below