Watch: UK weather: More storms to come after heavy rainfall, lightning and hail 'the size of peas' batter parts of country
Yellow weather warnings from the south-west and south-east of England have been issued by the Met Office, from Thursday through to Friday.
It has also warned that high winds could cause roof tiles to be ripped off and buildings to be damaged - with roads, rail and ferries potentially impacted by the conditions.
The national forecaster warned lives could be lost in the freak weather.
In a warning issued on Wednesday, it said: “There is a small chance that injuries and danger to life could occur from large waves and beach material being thrown onto sea fronts, coastal roads and properties.”
Several yellow rain and thunderstorm warnings remain in place on Wednesday for Northern Ireland, northern England and parts of Scotland.
Northern Scotland is likely to be hit by the worst of it, with an amber warning predicting fast flowing flood waters.
The Met Office added: “Thunderstorms have developed across parts of the north Midlands and northern England this afternoon and are expected to continue until early evening.
“Whilst some places will remain dry, a few locations are likely to see 20-30 mm of rain fall in an hour. Additionally, hail up to 2cm in diameter is possible as well as frequent lightning.”
Flash flooding sparked closure at stations and chaos at hospitals.
London Fire Brigade (LFB) had taken more than 1,000 calls by the early hours of Monday morning following the torrential rain and thunderstorms.
Barts Health, London’s largest health trust, declared a major incident after water flooded the basement at Whipps Cross Hospital, causing damage to the electrical system. Newham Hospital was also affected.
All scheduled surgeries and outpatient appointments at Whipps Cross were cancelled and ambulances diverted.
Earlier on Wednesday, Trafford General Hospital was struck by lightning causing a fire on the roof of the building on Wednesday.
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