London weather: Thunderstorm alert raised to severe as capital warned of 'significant flooding' threat

London is facing the threat of “significant” flooding which could even pose a danger to life as thunderstorms batter the UK.

An amber warning for thunderstorms has been issued for between 4am and 11am on Saturday, spanning major towns and cities including Brighton, Portsmouth, Chelmsford, St Albans and Cambridge, as well as the capital.

Forecasters have warned of sudden flooding in roads and homes with some more remote communities at risk of being cut off, while delays to train and bus services are also likely.

Power cuts could also occur and buildings are at risk of damage from floodwater, lightning strikes, hail and strong winds.

A yellow alert is also in place for a huge swathe of England from Northumberland to the South Coast, lasting from 9pm on Friday to 6pm on Saturday.

During that time, parts of north-east England such as Durham, Middlesbrough and Yorkshire could see up to 25mm of rain in less than an hour, as well as frequent lightning and large hail.

In the south, rain is predicted to be torrential, with up to 30mm falling in less than an hour, and 100mm in just a few hours in certain places.

Gusty winds, frequent lightning and hail are also likely.

The Met Office warns: “Areas of heavy, thundery rain may lead to disruption to transport and travel from late Friday through much of Saturday.”

It adds: “Flooding of homes and businesses could happen quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds.

“Fast flowing or deep floodwater is possible, causing a danger to life.

“Some communities might become cut off if roads flood.”

It comes as Londoners are set to swelter in 30C on what looks set to be an uncomfortably humid day on Friday.

Forecasters say the high temperatures will not last as long as the earlier summer heatwaves.

BBC Weather is predicting thunderstorms will sweep over London on Saturday, Sunday and Monday - as the hot weather breaks with daytime highs of between 21C and 24C.

Across other parts of the UK temperatures will climb to 28C with a chance of 29C on Thursday, before peaking at a potential 30C in London on Friday, Met Office meteorologist Jonathan Vautrey said.

Mr Vautrey said: “We’re starting to see south westerly winds come in, that’s bringing in hotter and more humid conditions, particularly in southern areas, we are going to see temperatures climbing again.

“There is the potential for 30C around the London region by the time we reach Friday, other areas around south east England will push towards high 20s.

“Average temperatures in July for the south east is around 23C, so it will be about 5C above average.

“On Thursday it will probably creep up to around 28C in London, maybe 29C in more central England.

“Friday is looking to be the peak of the current hot spell.

“This heat is not going to be as widespread as what we’ve just come out of, areas to the north aren’t going to be seeing the same highs.

“The heat we had last time was home grown, it wasn’t that humid, but because this heat is coming in from the south westerly direction, it is more humid. It’s going to be feeling more sticky.”

There is a “small probability” a localised area manages to get the three-day category for a heatwave this week, but for most people it will be more of a “hot spell”, Mr Vautrey added.

It comes as Southern Water has become the latest company to bring in a hosepipe ban, to protect rare chalk stream habitat, as England battles exceptionally dry weather.

The company said restrictions on hosepipes for activities such as watering gardens, filling paddling pools or washing cars would come in for households in Hampshire and the Isle of Wight from Monday.

It is the latest announcement by water companies bringing in hosepipe bans in response to the driest start to the year since 1976 for England.

Rainfall across England was 20% less than the long-term average for June, which was also the hottest on record for the country, with two heatwaves driving unusually high demand for water, the Environment Agency has said.

Drought was declared in East and West Midlands on Tuesday, with the region joining swathes of northern England in drought status.

Yorkshire Water became the first major water company to bring in a hosepipe ban which came into effect last Friday.

South East Water has announced a hosepipe ban in Kent and Sussex from Friday, and Thames Water is bringing in a ban from next Tuesday for customers in Oxfordshire, Gloucestershire, most of Wiltshire and some parts of Berkshire.