The British capital ground to a halt on Monday after the worst snowstorm in 18 years caused hundreds of flight cancellations and virtually shut down public transportation.

Shops, schools and courts shut down and long trails of commuters trudged through the streets, looking for scarce taxis or ways to work after more than four inches of snow fell overnight.

"We're not in Russia here," said Guy Pitt, a Transport for London spokesman. "We don't have an infrastructure built for constant snow."

Heathrow closed one of its two runways and reported more than 650 cancellations. Major delays and cancellations were also reported at London's other major airports at Gatwick, Luton and Stansted. London's City Airport was closed.

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An Airbus 330 coming from Cyprus slid off the taxiway at Heathrow with 104 passengers on board. Cyprus Airways spokesman Kyriakos Kyriakou said there were no injuries or damage. No other incidents were reported.

There were massive traffic jams on many highways near London.

The Met Office, the country's national weather service, said it expected another four inches Monday afternoon.

"We are doing everything in our power to ensure that the services — road, rail and airports — are open as quickly as possible and we are continuously monitoring this throughout the day," said Prime Minister Gordon Brown.

London Mayor Boris Johnson said the city lacked snowplows.

"You can grit and you can salt it but the snow comes down again," he said. "You can make an investment ... in snowplows for London and then not use them for a couple of decades."

Johnson said many buses couldn't be sent out because "if they skid they become a lethal weapon."

London's subway network was hit hard because much of the system is above ground. Of some 12 lines, only the Victoria Line was unaffected.

After waiting in vain for an Underground train to arrive, office worker Caroline Samuel, 36, decided to retreat.

"There's no point in going to work today," she said. "I'm going home."

Many of the tracks were covered in snow or ice and some transport workers themselves struggled to get in to work.

Heavy snowfall in France also disrupted traffic and caused delays at Charles de Gaulle airport in Paris.

Southeast England was hardest hit with up to 10 inches reported in some areas.