The big freeze continues as PM backs Heathrow's decision to cancel flights

Forecasters issue snow warnings as sub-zero temperatures and ice spread westwards

Forecasters warned that winter is expected to grip much of Britain for the rest of the week as Downing Street defended Heathrow's decision to cancel hundreds of flights over the weekend before a snowflake fell.

The Prime Minister's spokesman praised the Spanish-owned operators BAA, which scrapped half of its 1,300 flights – many of them in advance of Saturday's 2.4in (6cm) dusting.

Britain's international air hub was severely criticised last year when arctic conditions led to chaos as passengers waited days for their planes to take off.

Instead, as it faced its first severe test of the winter, Heathrow put its "snow plan" into action, cancelling a third of flights in advance to prevent repeat scenes.

"One noticeable thing was that we didn't see those very long queues snaking out of the airports, because of the decisions that had been made," said Mr Cameron's spokesman, who was forced to fend off claims that Britain's main air link had been caught on the hop again.

The Met Office said it had been able to pinpoint the arrival of snow at Heathrow to within 10 minutes. Meanwhile other airports in Scandinavia and mainland Europe remained relatively unhampered despite temperatures plunging to as low as -27C.

Temperatures are likely to plummet to -9C in parts of northern England tomorrow night, according to forecasts.

On the roads, ice and freezing fog were the biggest problem. A 25-mile section of the A1 in North Yorkshire was closed when lorries jackknifed.

Three teenagers were badly hurt on Saturday when a car mounted the pavement on a steep hill in Bishop Auckland, County Durham, after skidding on ice.

Police warned against people going into icy water after a 51-year-old was pulled to safety after jumping into the River Wansbeck in Morpeth, Northumberland, to rescue a stranger's dog.

The RAC had the busiest February weekend in its history, with 41 per cent more calls than usual. But Network Rail said the snow had had no significant impact on services.

Most schools opened although about 60 secondaries and primaries in Kent and East Sussex remained shut.

In Sandwell, in the West Midlands, dozens of residents took to the streets to clear the snow. They had obviously heeded the Department for Communities' advice to people not to "believe the myths" that they could be sued if someone slipped on a path they had cleared.

The Met Office said sub-zero temperatures and widespread ice were expected to spread westwards and issued snow warnings for eastern England.

Arctic Britain: five-day forecast

Tuesday: Widespread risk of ice as temperatures plunge below zero overnight. Snow will threaten eastern areas but most places will be bright and sunny.

Wednesday: Sunny and very cold but with chance of snow along eastern coastline.

Thursday: Rain spreading from Northern Ireland and Western Scotland could bring snow to northern England. Cloudier elsewhere but still very cold.

Friday: Very cold and continuing threat of snow in the east. Milder in the west.

Saturday: Still cold but becoming more unsettled as the weekend continues, temperatures returning to seasonal average.