Tens of thousands of homes are without power after Storm Desmond caused severe flooding and travel disruption across northern England and parts of Scotland.
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 nearly 50 severe flood warnings remain in place.
Prime Minister David Cameron said the government was doing all it can to help people and prevent further damage.
Mr Cameron will chair a meeting of the Cobra contingencies committee on Monday to co-ordinate the emergency response.
"I would like to pay a huge tribute to all those emergency workers and troops who have worked tirelessly to respond to this weekend's events," he said.
"There has been a tremendous response from local communities too, with people taking in families affected by the flooding."
Provisional figures suggest more than 340mm of rain fell in 24 hours in the Lake District. The current record is 316.4mm of rain over the same time period at Seathwaite, Cumbria, in 2009.
In Cumbria, where a major incident was declared, emergency crews used boats to carry people to safety and eight rescue centres are open for those forced to leave their homes.
Rescue teams from the Royal National Lifeboat Institution evacuated homes in Carlisle, helping around 200 people.
In other developments:
- Search teams are trying to find an elderly man thought to have fallen into flood water in Kendal
- Nearly 50 severe flood warnings - indicating risk to life - remain in place in northern England, as well as more than 30 flood warnings
- Electricity has been restored to 11,000 homes in Lancaster by a generator with 44,000 more expected to be restored by Monday evening
- In Scotland about 40 flood warnings and alerts are in place, and some main roads are closed due to landslides and flooding
- About 70 households are still without power in north Wales, after 700 lost power on Saturday
- There are no trains running between England and Scotland via Preston, while road restrictions are in place on the A66 and other routes
- Two hospitals - Cumberland Infirmary and Royal Lancaster Infirmary - are being powered by back-up generators, resulting in non-emergency operations and clinics being cancelled on Monday
- Pooley Bridge in Ullswater, and the Fitz Footbridge, in Keswick, have both collapsed. It follows the collapse of another bridge near the village of Braithwaite, on Saturday
- Footballers from Carlisle United have offered to help people in the city affected by flooding
'We were about to sell our house'
Roger and Julie Scoon, of Keswick, put their furniture in a room that was safe during the 2009 floods - but this time around the water came in through the windows.
"We did what we could, we got flood gates, we put tiled floors down so we can mop out, but we never dreamt it would come up here," Mr Scoon added.
The couple, who had been due to sell their house when the flooding hit, said of where they would be for Christmas: "We can't think that far ahead... we'll just take it a day at a time really."
John Chadwick was helped from his home in Carlisle.
"I was evacuated as the River Caldew burst over the flood barriers.
"I live alone and have severe mobility problems including osteoarthritis and mild epilepsy - I just had time to grab some medication.
"I have nowhere suitable to stay as I need ground floor accommodation with disabled access. Social services informed me that they were inundated and I would just have to rough it out at a friend's place a short distance away.
"The waters were 2in deep and I got out by dinghy."
In 2010, a £38m flood defence scheme for Carlisle - which has seen some of the worst flooding - was completed in a bid to protect about 3,000 homes and businesses around the city.
Floods minister Rory Stewart said defences - which have been criticised - 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, Mayor of Keswick 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.
The Met Office has issued fresh yellow warnings for rain next week for many badly affected areas.
Storm Desmond is the fourth storm to be given a name by the public in a project by the Met Office and Met Eireann in Ireland to help raise awareness of severe weather.
Live flood warnings from the Environment Agency and the Scottish Environment Protection Agency.
Note: the Environment Agency and the Scottish Environment Protection Agency display their flood alert data differently. While the Environment Agency highlights individual rivers only, in Scotland the entire region is coloured to indicate the level of alert.
This map and flood alert data are supplied to the BBC by third parties. The BBC is not responsible for its accuracy and you use it at your own risk.