The heaviest snowfall to hit the UK in 18 years has brought travel chaos to large parts of the country.

Thousands were left stranded as air, rail and road services suffered severe delays and thousands of schools across the country were closed.

Conditions looked set to worsen overnight with forecasters predicting temperatures will plummet to -6C as the snow moves to the North.

An army of snow ploughs and gritters is working around the clock to clear roads, but motorists, who were warned only to make essential journeys, were caught in tailbacks of more than 50 miles and queues of up to two-and-a-half hours.

Earlier, major airports closed runways, all bus services were cancelled in London during the morning rush hour and dozens of trains - including all Southeastern services in and out of the capital - were suspended.

London Mayor Boris Johnson defended the decision, saying that "unleashing a 12-tonne bus on to heavily packed snow or ice" would risk "turning it into a lethal weapon".

On the London Underground, ten of the 11 lines were either completely or partly suspended as a Transport for London spokesman blamed the "quantity of snowfall" for the extent of the disruption.

Prime Minister Gordon Brown said the authorities are doing "everything in our power" to ensure the resumption of key transport links after a number of train services linking London and the south coast were disrupted.

A snapshot survey of more than 300 employers found one in five adults had stayed away from work today because of the extreme weather.

Mr Johnson praised those who turned up to work for helping to keep the capital moving and suspended the city's congestion charge scheme as a thank-you gesture.

More than 11cm of snow fell at Heathrow Airport, 25cm over the North Downs in Kent and Surrey, 8cm along the eastern side of the Pennines and 1cm across the Welsh border.

More than 1,000 primary and secondary schools were forced to shut their doors due to the adverse weather conditions. Schools in southern England were among the worst affected.

At Heathrow Airport, a Cyprus Airways flight, CY 332, from Larnaca strayed on to a grassed area while taxiing to the terminal building in the snow after landing shortly after 8.30am. None of the passengers were injured.

Nearly 800 flights were cancelled at Heathrow and others were subject to long delays. About 200 Ryanair flights into and out of the UK were cancelled, mostly at Stansted, and all BA flights from Heathrow were cancelled until 5pm.

Air passengers could face a second day of flight cancellations and delays on Tuesday as more snow is on its way, airlines said.

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