Britain needs to face up to a radical change in weather conditions that could be the result of global warming, and spend much more on flood defences, Sir David King, the government's special envoy on climate change, has said.

Amid the worst floods for decades, King said the UK must do more to manage the problem, potentially doubling spending to £1bn a year by 2020, as extreme weather events are likely to become more frequent.

The former chief scientific adviser spoke out as the UK braced itself for further disruption from wind and storms, with 84 flood warnings in England and Wales, and a further 220 areas on alert.

The storms and floods have claimed three lives, including that of a man thought to have drowned after his mobility scooter fell into the river Thames at Osney in Oxford on Saturday night. A teenager remains missing in Devon.

Strong winds, persistent rain and tidal surges are predicted for the UK for at least another two days, mostly in the south and Wales, as emergency services attempt to cope with the trail of devastation already caused by the severe weather.

On Sunday, the Met Office issued yellow weather warnings of ice and rain, predicting river and surface flooding as well as travel disruption, mainly in south Wales, the south-west and south-east of England, Northern Ireland and Scotland. Up to 40mm of rain could fall on higher ground.

Coastal areas – particularly in southern England – are most vulnerable on Monday because of unusually high tides and the arrival of a strong Atlantic storm. The Thames barrier will remain closed to protect land near the river.

Inland rainfall is expected to put pressure on rivers, endangering nearby communities including those along the river Medway in Kent, the Severn estuary in Gloucestershire and the Thames in Oxford.

King raised the possibility that the storms are linked to climate change and said "priority should be given to much more funding to create a better situation so we can face up to flooding in a proper manner on the British Isles.

"The important thing to get across is the simple notion that storms and severe weather conditions that we might have expected to occur once in 100 years, say, in the past may now be happening more frequently," he told BBC Radio 5 Live.

"And the reason is – as predicted by scientists – that the climate is changing and as the climate changes we can anticipate quite a radical change in weather conditions."

King said a report he wrote in 2004 predicted that a sea-level rise, increased storm surges and increased intensity of rainfall would penetrate further inland, affecting cities and causing billions of pounds a year of economic damage. The Environment Agency estimated then that for every pound invested in flood defences the country would save about £7 or £8 in flood damage, he added. But a boost in funding for defences did not survive the recession.

"If we really want to manage this problem, and I'm sure that all of us do, we will have to do two things," he said. "One, get back to the higher investment level in flood defences and, two, push hard on the rest of the world in terms of mitigating the impacts of climate change and of course this is a big target for getting an international agreement."

Thousands of people have lost power and about 200 have seen their homes flooded over the past few weeks, putting David Cameron under pressure over cuts to the Environment Agency's budget.

On Sunday the prime minister insisted the UK would see record levels of spending on flood defences "guaranteed right out into 2020 so [the Environment Agency] can really plan for the future".

However, Labour accused Owen Paterson, the Conservative environment secretary of ignoring the increased risk of flooding because he is sceptical about climate change science.

Maria Eagle, the shadow environment secretary, said Paterson had questions to answer about why he was allowing cuts at the Environment Agency that could affect Britain's ability to deal with severe weather incidents.

Paterson chaired another meeting of the government's emergency committee "to ensure everything is being done on the ground to prepare for bad weather ahead".

Matt Dobson, a forecaster for MeteoGroup, said the rain "simply has nowhere to go" because weeks of severe weather had left the ground waterlogged and rivers rising over their banks.

"It's very unusual to have so many powerful storms come in one after the other in such a short space of time; we haven't seen anything like this since about 1991," he said.