A band of heavy rain brought misery to homeowners, holidaymakers and businesses after flash flooding left scores of properties under water.
Parts of south-west England and Wales were among the worst hit, as the Met Office issued a severe weather warning ahead of further heavy rainfall.
Forecasters say there is a prospect of more flooding, particularly in urban areas, although the worst of the weather is expected to give way to dry spells by Tuesday, and temperatures around 23C (73.4F) in London.
Some weather gauges have reported more than 10mm of rainfall in just an hour, including Culdrose in Cornwall (11.2mm) and Liscombe on Exmoor, where 10.6mm fell at lunchtime. Emergency crews have been called in to help the worst affected, with recovery company Richfords reporting a ten-fold increase in call-outs for an average August day.
Up to 60mm (2.3ins) of rain is possible in the south west of England, with warnings that West Yorkshire could also be hit.
Sean Penston, a forecaster with MeteoGroup, the weather division of the Press Association, said: "We've seen quite a few showers in the last few days, which has helped to soften the ground. But the heavy rainfall means there has been a chance of flooding, particularly in urban areas where there's a lot of rainwater run-off collecting with nowhere to go. The rain will gradually clear overnight and it should be fairly dry most places (on Tuesday)."
Cornwall Fire and Rescue Service said there had been isolated incidents of flash flooding in the Porthleven, Perranporth, Redruth, Camborne, Bolingey, Newquay, Truro, Falmouth, Bude and Bodmin areas, which crews had responded to.
Mike Cooper, a director with Cornwall-based recovery firm Richfords Fire and Flood, said they had been inundated with calls for help at more than 20 properties, including a school. He said: "We would normally have one or two calls a day during August, but we've had more than 20 so far today, and are expecting several more tomorrow once we hear from insurers."
Western Power Distribution said its engineers were attempting to restore electricity to more than 500 properties in the St Teath area of north Cornwall, while the flooding also caused the closure of the minor injury department at Newquay Community Hospital.
The Met Office issued yellow warnings for rainfall, while Natural Resources Wales has put out more than a dozen flood alerts.