Two weeks’ worth of rain have fallen in just 24 hours across the north, leaving cities such as Manchester under water.
Warnings are in place for more flooding across Yorkshire and Greater Manchester, while many parts of the UK could be hit by thunderstorms in the next 48 hours.
Driving conditions will be hazardous and roads may be closed due to floods, says the Met Office.
But Southern Water – which serves 2.3million customers across Kent, Sussex, Hampshire and the Isle of Wight – has applied for the first hosepipe ban since 2012.
Karen Gibbs, from the Consumer Council for Water, said: “People in the affected area would only be asked not to use hosepipes and sprinklers, which can use huge amounts of water.
“In the meantime we’d encourage customers to keep using water wisely and for Southern to do everything in its power to reduce the amount of water lost through leaking pipes – it should be leading by example.”
The water company has blamed falling river levels for the ban.
Forecasters are predicting more 30C heatwaves over the next few weeks.
● The 38.7C recorded in Cambridge last Thursday is officially the highest temperature ever in the UK, the Met Office confirmed last night.