Early alerts in Cornwall have spread as far as the Isle of Wight, with eight official warnings and 23 flood alerts put in place by the Environment Agency (EA) within three hours on Wednesday morning.
More bad weather is in prospect for at least a week and probably longer, according to the Meteorological Office, with May Day bank holiday looking like a opportunity for DIY indoors. But the rain will have to continue for weeks to replenish the exhausted aquifers of areas in drought, according to water companies.
None of the flood warnings has reached severe level, the EA's most serious, but homeowners close to rivers in parts of Cornwall, Devon and Somerset have been told to take "immediate" precautions, deploying any defences to hand and shifting valuables upstairs. A rollcall of the region's evocatively named rivers, including the Upper Axe, Lower Otter, Taw and Wriggle, are expected to break their banks during the day.
There are also concerns about seafront flooding at high tide in Torquay, Sidmouth and Exmouth as up to 40mm (1.6ins) of rain is forecast to fall by dusk. High winds accompanying the rain have blown down trees in some areas, with the added bulk of new foliage making them more vulnerable to sudden gusts.
Plans to crane into place the main steel beam of the new main road bridge at Workington, which was swept away in the floods of November 2009, have been delayed until next week because of the forecast of high winds.
Rainfall is also intensifying in Scotland and northern England, and moving south to link up with the south-western weather front to ensure the whole country is soaked by late on Thursday. The Met Office said a pattern had been established of wet fronts from the Atlantic rolling across the UK in bands, with longer range estimates suggesting this will continue for most of May.
A prolonged soaking will give some relief to water companies, whose drought measures began at almost exactly the same time as the previous, long spell of dry weather gave way to the new pattern. But Trevor Bishop, head of water resources at the EA, said that 18 months of below-average rainfall needed almost as much time to catch up.
"It's going to take more than a week or two of rain," he said. "This is good for farmers and gardeners and the cooler temperatures ease the pressure on fish and wildlife in rivers and lakes. But with the soil so dry, most of the current rain will be soaked up. Or, worse still, it will run off quickly in places where the soil has been compacted, and cause flash floods."
Either way, only a small amount of the downpour will get through to sunken groundwater levels, to start the long-term process of topping up.
In Scotland, the risk of flooding is heightened by snow-melt as the rain sweeps across the Highlands. The Met Office said there would be occasional sunny spells across the country and temperatures would reach 11 to 13C in places, but added: "There is no real end in sight to this unsettled period of weather.
"We'll certainly see showers across the country in the next seven days and longer forecasts suggest it will continue through much of May."
She added the showers would be broken by occasional sunny spells with average temperatures of between 11 and 13C.
The Queen and the Duke of Edinburgh donned coats and macs on a visit to London's docklands to name the ornate barge, Gloriana, which will lead a 1,000-strong flotilla up the Thames during the diamond jubilee pageant in June. Lord Sterling, the project's head who also organised golden jubilee celebrations in 2002, thanked both for "bracing the inclement weather".
Humbler citizens are proving less stoic, according to travel companies, which report a surge of holiday bookings to escape the newly dismal weather. Virgin Atlantic and lowcostholidays.com report rises of between 37% and 60% for warm weather overseas resorts, compared with last year.