The Army was this afternoon ready to save hundreds of York homes if flood defences were breached.

They are on call to use thousands of sandbags to strengthen the city's river defences.

Meanwhile, drivers faced rush hour misery following the closure of key routes due to flooding, with the city's highways boss calling the congestion the worst he had ever seen.

The Ouse peaked at 16ft 5ins today, its third highest level in a century, just inches short of "overtopping" York's defences.

A sandbagging operation involving 280 soldiers and 40 vehicles - including tracked ones - was cancelled last night when emergency planners calculated that their "worst case scenario" would not happen.

But with heavy rain falling on the city and in the Dales area which feeds into the Ouse it was confirmed that troops remained available if the river again threatened to breach the defences.

John Simmons, City of York Council's emergency planning co-ordinator, said one of the options to combat flooding last night involved soldiers from Imphal Barracks using some of the 10,000 sandbags available in the city to place along the top of the flood walls and banks.

The troops would also have been used to help evacuate residents. Weather forecasters said North Yorkshire was "very unlucky" today after being lashed with an unexpected band of showers.

While other northern areas remained dry, York and the Pennines were hit with torrential rain, causing fears that floodwaters would continue to rise.

More heavy rain is expected tomorrow afternoon, with storms predicted for Sunday.

City of York Council urged motorists to avoid the city centre unless absolutely necessary as floods led to mounting traffic problems on key routes, with the A19 at Fulford and Tower Street closed.

Peter Evely, the council's head of highways, said the closure of the A19 south of the city and the closure of the A166 at Stamford Bridge was forcing traffic on to the A1079 from Wilberfoss. The A1079 was full in both directions with severe congestion.

The area around Grimston Bar on the A64 and on the slip road was heavily congested.

The only way into York was around the northern part of the city.Mr Evely said: "The congestion in and around the city is some of the worst I have ever witnessed in my time in York."

Lendal Bridge has been reopened to all traffic for the duration of the crisis.

Villages near York, including Cawood, Naburn, Buttercrambe and Acaster Malbis, were marooned. Flooding also hit Elvington and Breighton, while at Bolton Percy floodwater was lapping the doorsteps of several houses.

A council spokesman said two homes in Naburn had been sandbagged, as had between 20 and 30 homes in the city.

Pupils and teachers pulled out all the stops to get to Naburn Primary School.

Some 43 children out of 70 managed to struggle in, some in dinghies others on bicycles, until lunchtime, when the school was forced to close.

City Screen, in Coney Street, is closed until further notice.

New Walk Orchard Caravan Park, in Fulford, was under two feet of water.

York's bus services were being diverted in places.