Tens of thousands of people in Carlisle are still without power and others have been evacuated after heavy flooding.
The floods saw boats used by rescue workers
More than 3,000 people have already been moved to safety with a further 3,000 homes at "great risk" and more than 70,000 homes are without power.
Northumberland, North Wales and Scotland are among other areas worst hit and a spate of accidents has shut roads all over Britain.
Environment agencies have issued more than 100 flood warnings on UK rivers.
Among them are two severe flood warnings of imminent danger to life and property - for the River Eden, Carlisle, and the River Caldew, in nearby Denton Holme.
The bodies of two women were found in their homes in Carlisle, although it was not known whether they died due to the flooding.
There were reports in Scotland and Bradford of people being swept away.
On Scotland's west coast, a ferry ran aground with the 100 people on board set to remain overnight.
Police say Carlisle is completely cut off, with no safe roads in or out, and they have been appealing for help from boat owners because cars are unable to reach central areas.
A spokesman said water levels had peaked at 1545 GMT, at one metre higher than those seen in 1968 when Cumbria was last struck by serious flooding.
Helicopters had rescued at least 15 people, including children, from roofs in the area with the RAF on standby to airlift up to 8,000 more to safety, she added.
Motorists across the UK are being advised not to make journeys unless absolutely necessary and farmers are being told to move livestock to higher ground.
As well as those in Carlisle, hundreds of thousands of people across the country have been without power.
In the north-east, 150,000 homes suffered power cuts with 90,000 restored by Saturday night.
Central Networks, which distributes electricity throughout the Midlands, said 84,000 homes and businesses had been affected overnight with about 9,000 still cut off.
MAJOR ROADS CLOSED
M6 southbound, J44-43, J27, northbound J5-6
M1 northbound J26, southbound 27-26
M4, Severn crossing at Bristol
A66 at Eden Bridge, Cumbria
A591 in Kendal and part of the A69
A1M, J58-63 in both directions
No safe routes in or out of Carlisle, say police
A435, westbound at Clifton, Notts
QE2 Bridge at Dartford, Kent
A68 at Jedburgh and a section of the A6088 closed as well as a number of minor roads in the Scottish Borders
A832 in the Highlands
Southern Electric said 5,000 people in Oxfordshire, Berkshire, Hampshire, Wiltshire and the Isle of Wight are also without electricity after power cuts which, at their peak, saw 20,000 people cut off.
Major bridges around the country have been closed or restricted, and some train services have been severely disrupted.
In Haydon Bridge, on the Tyne, 40 people were taken from their homes to temporary shelter in a village school after the south Tyne burst its banks.
Ring Floodline on 0845 988 1188 for up-to-date flooding information.