Heavy snow has forced the closure of runways at airports in southern England and Wales, as bad weather caused commuter chaos at the height of the morning rushhour.

Four airports serving London -- City, Gatwick, Luton and Stansted -- shut runways, as did Birmingham, Bristol, and Cardiff in south Wales as up to 10 centimetres (four inches) of snow fell.

London's main Heathrow airport, west of the capital, was open, but British Airways said it was preparing to cancel some short-haul flights from about 1000 GMT.

Bosses at the airports affected were advising passengers to turn up as normal but to expect delays while runways were cleared.

Britain's Met Office weather centre issued a severe weather warning for England, Wales and Northern Ireland on Wednesday. The forecast is for up to 15 centimetres of snow in parts on Thursday and five centimetres in London itself.

A forecaster for MeteoGroup UK, the weather division of Britain's domestic Press Association news agency, described the weather as "the most widespread snow event of the winter."

"We just haven't had this sort of thing in recent years," he added.

The snowfall -- an increasingly rare event outside mountainous areas of Britain -- also led to school closures, gridlock on the roads, plus disruption on London's underground train system and some mainline train services.

The weather was expected to move north-westwards towards Manchester and Liverpool later in the day, with freezing fog and black ice possible in areas already hit by snow, forecasters said.

The director-general of the British Chamber of Commerce, David Frost, has warned that the total economic impact "will be huge," as commuters would be hardest hit.

"It is expected that the lateness and loss of work hours caused by transport disruptions will cost the British economy up to 400 million pounds (605 million euros, 788 million dollars)," he said.

"This situation highlights the need for a real change in the current UK travel infrastructure."

Many travel operators issued advance warning to passengers to expect delays, despite warnings from London's transport watchdog that there was "no excuse" for major disruptions.

For those driving to work, the Highways Agency said that 400 salt-spreading vehicles were on stand-by to combat the snow, and advised drivers against travel unless they absolutely had to.

Westminster City Council, which is responsible for the Houses of Parliament and the City of London, the capital's finance centre, itself stockpiles 1,500 tonnes of salt, along with 50 pedestrian-operated salt spreaders.