An elderly woman was found dead in her flooded home in the tiny Welsh city of St Asaph on Tuesday after the nearby river burst its banks on the seventh day of torrential rains across Britain.
The Environment Agency urged residents to evacuate 500 homes in the deluged cathedral city in north Wales, after the River Elwy reached a record high and surged over flood defences.
Prime Minister David Cameron visited flood-hit areas of southwest England, where two other people have been killed since high winds and heavy rains began battering the country last Wednesday.
Police said the body of the elderly woman was pulled from her home by emergency workers at midday on Tuesday.
"An investigation is under way," a police spokesperson said. "There are no suspicious circumstances and the death is currently being treated as unexplained."
The Environment Agency had issued two severe flood warnings in Wales, including one in St Asaph, indicating a risk of death.
The agency said the River Elwy had reached a record level of 4.35 metres and was still rising.
Water was waist-height in some parts of St Asaph, an AFP photographer said.
Although it has a population of just 3400, St Asaph was awarded city status this year to mark Queen Elizabeth II's diamond jubilee.
Around 900 Britons have already abandoned their homes in addition to the 500 in St Asaph who have been advised to leave, while Britain's road and rail network have suffered days of chaos.
In the village of Buckfastleigh in southwest England, which is recovering from weekend floods, Cameron defended his government's cuts to the flood defence budget.
"We are spending over £2-billion ($3.2-billion, €2.5-billion) on flood defences over the current four-year period, which is six percent less than was spent over the last four years," he said.
"As well as that, we are actually encouraging private and other money into flood defences."
He praised flood-hit communities for their bravery in "traumatic" circumstances and vowed to ensure their insurers paid out.
The Environment Agency said the rain was set to ease off in the next two days but warned that, with the ground already saturated, any further wet weather could prolong the chaos.
In southwest England, a man died in Somerset on Friday when he became trapped in his car in rising waters and a woman was killed by a falling tree in the city of Exeter.
More than 180 flood warnings were still in place on Tuesday across England and Wales.
The Association of British Insurers said on Monday that up to 200 000 homes may be left without adequate cover due to a row with ministers over how future flooding costs will be paid.
Cameron vowed on Tuesday to take a "tough approach" in negotiations with insurers.
"I'm sure we will do a deal," he said.
Swathes of Britain were hit by floods in 2007, causing damage costing an estimated £3-billion.