LONDON's heaviest snowfall in 15 years has closed airports, shut 150 schools and caused major Tube disruption.
Hundreds of flights were cancelled at all five airports around London, while the average speed on motorways was reduced to just 30mph.
Schools in Barnet, Brent, Bromley, Croydon, Harrow, Hillingdon, Hounslow, Redbridge and Waltham Forest were among those that shut their gates for the day as the snow lay up to 10cm (4in) deep.
Across the country, more than 1,000 schools closed for the day - including 600 in Wales; 400 in Birmingham; 175 in Gloucestershire; 300 in Herefordshire and Worcestershire; 200 schools in Essex, 100 in Cambridgeshire and up to 100 in Norfolk and Suffolk.
The snowfall, thought to be the heaviest since 1991, started at around 3am and carried on until noon.
Much of it coincided with the morning rush hour before moving north-eastwards towards Liverpool, Manchester and Derby. Hilly areas saw as much as 15cm (6in), the Met Office said.
Despite overnight works to keep Heathrow airport open, more than 100 flights were still cancelled. Gatwick grounded at least 40 flights, while City Airport also suffered delays.
Both Luton and Stansted were closed for the whole morning. At the latter, about 100 flight were cancelled while 40 snow-clearing vehicles scooped up half a million square metres of snow.
Further afield, Cardiff, Bristol and Birmingham airports have also closed runways.
On the Underground, signal failures and faulty trains caused four lines to be part-suspended for most of the morning rush hour. Much of the affected sections on the Bakerloo, Jubilee, Piccadilly and Northern lines were on open track.
There were also severe delays throughout the day on the Metropolitan, Circle and Hammersmith & City lines.
Although all railway lines remained open throughout the day, Network Rail said most services ran with delays of 20 minutes
Frozen points caused delays and cancellations on trains into London run by Silverlink, South West Trains, Southern and Southeastern.
Midland Mainline cancelled some evening services, affecting commuters to the northern Home Counties. Virgin and First Great Western also revised their services.
An AA Roadwatch spokesman said London saw some of the worst driving conditions in the country, along with Surrey, Buckinghamshire, Hertfordshire and Essex.
Although the average speed on the UK's motorways was only 30mph, there were just 110 incidents instead of the usual 160, the traffic information service Trafficmaster said. A spokesman put it down to drivers being extra careful not to skid.
On the M25, snow prompted early morning lane closures near St Albans in Hertfordshire. During the morning rush hour, problems on the A22 near Croydon spilled over into a two-mile tailback on the London orbital.
Several centimetres of snow was removed from the A10 between the M25 and Shoreditch, while a snow plough had to clear streets in Islington, north London.
The Highways Agency said it had 400 gritters ready for roads across England. It advised drivers to make only essential journeys in bad weather and to take warm clothes, food, water, boots, de-icer, a torch and a spade along.
An AA poll of more than 1,000 drivers showed more than a quarter (26%) of motorists admitted driving off wearing just a t-shirt, regardless of the temperature outside.
One in 10 men admitted they have driven wearing nothing but their underwear.
£400m cost to economy
The day's transport delays would cost the British economy £400 million, business leaders warned. "The impact of this weather forecast on Britain will be huge," said David Frost, head of the British Chambers of Commerce. "This situation highlights the need for a real change in the current UK travel infrastructure."
Geoff Pope, chair of the London Assembly transport committee, said there was "no excuse" for major transport disruption due to bad weather.
"The Met Office has given ample warning of snow, and one would expect that Transport for London has taken steps to ensure that trains can still run without disruption."
- Rail passengers can get the latest service information on www.nationalrail.co.uk/badweather.
Drivers can check road conditions on the Highways Agency website or by calling the information line on 08457 504030.