Dangerous floods are set to hit parts of the UK amid thunderstorms lashing the country, the Met Office has warned.

It comes as Thames Water, which supplies 15 million people, is putting a hosepipe ban in place next week, saying water levels in its reservoirs were “much lower than usual”.

The Met Office has issued an amber thunderstorm warning covering most of the south east of England, including parts of London, from 11am until 10pm on Wednesday, meaning people should expect flooding and disruption.

The warning says: “Fast flowing or deep floodwater is likely, causing danger to life.”

Flooding is likely to affect homes and businesses “quickly”, as 30mm to 50mm of rain could fall in just an hour, while a few places may see more than 100mm in a few hours.

Forecasters say this could lead to train and bus cancellations amid difficult driving conditions, power cuts and communities becoming cut off from roads.

Lightning, hail and strong winds will also lash areas included in the warning, which spreads across Suffolk, Kent, Surrey and West Sussex.

Grahame Madge, Met Office spokesman said: “Heavy showers and thunderstorms will lead to some localised flooding and general disruption.

“Not everywhere will experience heavy downpours, or even see rain, but those affected areas could see 30mm to 50mm of rain falling in an hour.”

Parts of the UK have faced two days of heavy downpours and flooding, and a yellow thunderstorm warning has been in place across most of southern England, Wales and central areas, including the Midlands.

It warned of torrential, thundery rain until the end of Wednesday.

Doncaster and Bassetlaw Teaching Hospitals NHS Foundation Trust has asked people to only attend the emergency department if their condition is urgent or life-threatening, after water leaked into the building following heavy rain in Yorkshire on Tuesday.

A drought was officially declared across most of England following the driest July for 50 years and the driest first half of the year since 1976.

The Environment Agency has said it will take weeks of rain to replenish water sources and end the drought, as Thames Water joined Welsh Water, Southern Water and South East Water in implementing a hosepipe ban.

South West Water and Yorkshire Water will follow suit on August 23 and 26 respectively – meaning more than 29.4 million customers across the UK will be prohibited from using hosepipes by the end of next week.

In a statement on its website, Thames Water said: “We have more teams reducing leakage than ever before, working 24/7 to find and fix more than 1,100 leaks every week. The recent heatwaves mean that demand for water is also at record levels.

“We’ve been working around the clock to supply everyone, and customers have been brilliant at saving water where they can.

“But, with low rainfall forecast for the coming months, we now need to take the next step in our drought plan.

“Everything we do now will help protect supplies next summer and help the environment.

“We know these restrictions impact your day-to-day activities around your home and beyond, and we’re grateful for your support.”