Britain's emergency response committee has met after prolonged heavy rain caused widespread flooding in northwest England.

Photo: AFP

Tens of thousands of homes are without power after Storm Desmond caused severe flooding and travel disruption across northern England and parts of Scotland.

Police yesterday declared the storm a major incident, with hundreds of people forced to leave their homes.

Lifeboat crews and soldiers have been sent to help rescue stranded residents and tens of thousands of properties are without power in northern England and Scotland.

The rainfall is being described as extreme and unprecedented. Official estimates show a record 340 millimetres of rain fell in the Lake District and northern England in 24 hours.

The current record is 316.4mm of rain over the same time period at Seathwaite, Cumbria, in 2009.

Power at about 55,000 homes could be off for "days" following flooding at an electricity substation in Lancaster.

The army has been evacuating homes in Cumbria and the Scottish Borders, where hundreds of homes are under water and nearly 50 severe flood warnings remain.

The floods minister said the storm had "broken all the UK rainfall records".

"It's a completely unprecedented amount of water," Rory Stewart told BBC News.

Defences overwhelmed

In 2010, a £38m ($NZ85m) flood defence scheme for Carlisle was completed in a bid to protect about 3000 homes and businesses around the city.

Floods minister Mr Stewart said the defences had given authorities more time to evacuate people and kept flood levels down. The defences "held strong" but the huge levels of rain were too much for them, he said.

However, Keswick Mayor Paul Titley said the defences had been "completely overwhelmed".

"The flood defences were designed for a one in 100-year event and since it's six years since we had the last one, we were sort of surprised that we got one so soon," he added.

Britain has experienced several heavy floods in recent years.

In 2014, thousands of hectares of farmland in the south of the country were submerged for weeks, and the northwest region was badly flooded in both 2009 and 2005.

-BBC