LONDON, England (CNN) -- The worst snowstorm to hit Britain in 18 years forced the cancellation of more than 650 flights at London's Heathrow airport Monday and shut down the city's bus network, partially paralyzing the British capital. Heathrow, one of the busiest transport hubs in the world, closed both its runways for more than two hours Monday morning and operated with just one for the rest of the morning, according to BAA, the company which runs it. London City airport is also closed, while the British capital's other two airports, Stansted and Gatwick, were operating with severe delays, BAA said. British Airways canceled all flights out of Heathrow until 5 p.m. except for Edinburgh and Lisbon routes.
One of the city's largest cab companies was in such high demand it stopped taking cash and credit card bookings, serving only customers with accounts, it said. Dial-a-Cab, which has a fleet of over 2,500 vehicles, served mainly blue-chip companies trying to get employees into work, said Keith Cain a Control Room manager for the company.
Jochen Jaeger, 36, found himself stranded at Heathrow, unable to fly home to Zurich or to get back into the apartment he rented in London. "I will stay here at the airport," he told CNN. "There is no other option. I may have to spend the night here."
Jenny Leslie, a shop worker at Heathrow's Terminal 2, said it was so quiet at the airport "you can hear a pin drop."
Southampton Airport, southwest of London, was also closed for several hours Monday morning, but re-opened by noon (7 a.m. ET).
London's famous red buses were pulled off the roads on Sunday night as the snow got deeper. "Bus services were suspended throughout London last night on the grounds of passenger safety due to the unsafe road conditions resulting in a large number of traffic incidents across London," Transport for London, the city's transit agency, said. "Services remain suspended but we aim to restore services as soon as possible once roads have been treated and it is safe to recommence services."
The city's subway system was experiencing severe delays, leaving normally bustling central London something of a ghost town.
Snow in the Underground?
On a regular weekday, London's transit system handles more than three million passenger journeys.
The Federation of Small Businesses estimated that at least one in five workers nationwide -- about 6.4 million employees -- failed to make it into work Monday morning. But the figure was estimated to be far higher -- around two in five -- in London and southeast England, which is home to around a fifth of all British businesses.
Monday's disruptions are likely to cost businesses £1.2 billion ($1.7 billion), FSB spokesman Stephen Alambritis told CNN.
Britain's national weather service, the Met Office, issued severe weather warnings for all of England and much of Scotland and Wales for both Monday and Tuesday. It reported eight inches of snow in Balham, south London, and six inches at Canary Wharf in east London.
The last time such widespread snowfall affected Britain was in February 1991, the Met Office said.
The snow meant a break from school for the region's children as classes gave way to snowball fights. In the southern English seaside resort of Brighton there was a carnival atmosphere as dozens of people who were unable to get to work threw snowballs and built snowmen on the beach.
Mother-of-three Fiona Robbins, 45, added: "Everyone is very excited to be able to show their children proper snow for the first time."
Tuesday's forecast is expected to bring some relief, with the snow expected to stop and temperatures to rise above freezing.
Two climbers were found dead Monday morning on Snowdon, the highest mountain in Wales, after being reported missing Sunday night, North Wales Police said. It was not clear if their deaths were related to the storm.