London's Heathrow airport says it has cancelled 260 flight or 20% of its usual schedule because of snow and low visibility.

Sunday was the third day of flight disruptions at Heathrow, one of Europe's busiest airports, which has seen long lines and stranded passengers camped out on its terminal floors.

Airport operator said it had spent millions of pounds improving its ability to cope with icy weather conditions after the airport was virtually shut down by snow for several days in December 2010.

Forecasters say snow is expected to blanket Britain in the coming week.