A dusting of snow across the South East has caused transport chaos, temporarily closing a major airport and delaying road and rail journeys.
Forecasters said the snow had amounted to no more than "one or two centimetres in places", yet thousands of people's journeys were delayed.
Stansted airport in Essex was shut from about 6am to 8.30am, with passengers complaining they had been given incorrect information.
No trains were able to run between Watford Junction in Hertfordshire and Harrow and Wealdstone in North West London, while snow caused delays of up to 90 minutes between London and Reading in Berkshire.
Trains were unable to run between Barnes and Hounslow via Brentford in West London, while there were delays between London and Ashford International in Kent.
There were also delays on the London Overground, and the Metropolitan, Central and Bakerloo Tube lines, while a faulty train led to delays on the Victoria line.
The snow also caused significant transport problems elsewhere in the country.
National Rail has reported delays in Nottingham, Doncaster, Crewe, and Congleton in Cheshire, where a person was struck by a train.
The snowy conditions led to a crash involving ten vehicles on the London-bound carriageway of the A299 Thanet Way at Whitstable in Kent. Police say there were no serious injuries.
Essex Police said there were 78 crashes between 6am and 11.30am, injuring 13 people - one seriously.
Buses had to replace trains between Redhill in Surrey and Tonbridge in Kent. The A120 was one of the many roads in Essex to be affected by the weather. The A171 near Scarborough was one of Yorkshire's snow-hit routes.
The AA has attended more than 5,000 breakdowns, with a peak at around 8am of 1,300 an hour.
It said the Home Counties, particularly Essex, had been badly hit.
British Gas said it had put its 10,000 engineers on red alert as it expected to receive almost 250,000 calls for help from customers this week.
That is nearly 70,000 more calls than British Gas receives in an average week.
Meanwhile motorists in Scotland have been warned to prepare for difficult driving conditions on Thursday morning, with more snow forecast for much of the country.
The Met Office issued amber warnings of snow in the Highlands, Central, Tayside, Fife, Strathclyde and Grampian regions, and yellow warnings of snow for Orkney, Shetland and Lothian and Borders.
Sleet and snow are expected to spread in the early hours after a cold night with widespread frost.
Forecasters said four to six inches of snow is likely to fall on levels above 1,300ft and two to four inches is expected on areas above 650ft.
Travel networks are likely to be disrupted, especially over the M8 corridor to the east of Glasgow, across Perthshire and over much of inland eastern Scotland.