UK weather: When and where are major thunderstorm warnings?

Britons have been warned to expect travel delays and treacherous conditions on the roads as heavy downpours and thunderstorms are set to hit large parts of the country.

The Met Office has issued a yellow weather warning for thunderstorms, running on Thursday from 11.30am to 7pm.

Forecasters warn of potential delays to train services, driving conditions being affected by hail and sprays of water, and short-term power cuts.

The chance of some homes and businesses being flooded is "likely", according to the Met Office, and some buildings could also be damaged by lightning strikes.

Already it has been an especially wet month, with half of the average rainfall for May falling over several hours on Tuesday in parts of southern England.

Where are thunderstorm warnings in place?

The Met Office's yellow weather warning covers central and north London, large parts of Essex, Hertfordshire, Cambridgeshire, and Suffolk.

It also covers most of the East and West Midlands and most of Yorkshire and stretches as far north as Allendale, Northumberland.

Major cities, shown in the yellow zone of the Met Office's map, include London, Cambridge, Birmingham, Leicester, Nottingham, Sheffield, Leeds and York.

The warning for Thursday 11 May, currently runs from 11.30am until 7pm, with no warnings in place for the following day.

Driving in a yellow warning zone

The Met Office advises people to take care on the roads when driving through heavy wind, rain and thunderstorms.

Even moderate rain can reduce visibility, so as a rule of thumb, if you need to use your windshield wipers, you should also slow down.

Drivers are advised to wait for heavy downpours to clear before they set off if possible, and, failing that, to stick to main roads to avoid encounters with fallen branches and debris.

Motorists should be wary of strong gusts of wind unsettling their vehicles, slippery road surfaces, and the potential for sprays of water from nearby vehicles.

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"If the road is flooded, turn around and find another route. The number one cause of death during flooding is driving through flood water, so the safest advice is turn around, don’t drown," the Met Office says.

"Although the water may seem shallow, just 12 in (30cm) of moving water can float your car, potentially taking it to deeper water from which you may need rescuing.

"Flood water also contains hidden hazards which can damage your car, and just an egg-cupful of water sucked into your car’s engine will lead to severe damage."

Staying safe during a thunderstorm

Lightning can lead to power surges, which in some cases can damage electronic devices and start fires. The Met Office advises people to unplug any non-essential appliances before a thunderstorm hits their area.

Telephone lines can conduct electricity, so people are urged to avoid landline calls during a storm unless it is an emergency.

The Met Office advises people to seek shelter if possible, and failing that, to find a low-lying open place away from any trees, poles or metal objects that could be brought crashing down.

Avoid playing golf, rod fishing, or boating on a lake, and watch out for any metal objects that could conduct electricity, the organisation adds.

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If you find yourself in an exposed location it may be advisable to squat close to the ground, with hands on knees and with head tucked between them – especially if you feel your hair stand on end.

Try to touch as little of the ground with your body as possible, do not lie down on the ground, the Met Office advises.

If you're caught in a thunderstorm while driving on the road you should wind up your windows and stay inside your car.

This is because the frame of the vast majority of cars will act as a conductive Faraday cage, passing the current around the passengers inside and on to the ground – so stepping outside could put you at risk.

'Today has been on a different scale'

The latest warning comes after heavy rainfall in much of southern England earlier this week caused flash flooding that left roads impassable and homes battling a deluge of water.

Around half of the average rainfall for the month of May fell in torrential downpours over several hours, prompting rivers to burst their banks and house to be evacuated.

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In North Cadbury, Somerset, villagers reported up to 4ft of water following heavy rainfall on Tuesday that left families unable to use their homes. While in Tipton St John, the River Otter burst its banks and dumped "knee-high" water onto the roads, the BBC reported.

Val Coots, from Bathealton in Somerset, told PA: “The stream breaks its banks quite regularly after prolonged heavy rain, usually a couple of times per year.

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“Today has been on a different scale though, really unbelievable, the stream rose about a foot above the level of the garden and whole parts either side were completely submerged.

“You can see from one of the tweets what it looks like normally. The house is much higher, so we aren’t in any danger.”

Flooding conditions also shuttered roads and railways, with water covering thoroughfares in parts of Essex, Devon, Northamptonshire and Hertfordshire.