The Met Office has extended its first ever thunderstorm alert across more of the country with the threat of travel disruption and power cuts.

Sunday's yellow "be aware" warning for South West England and South Wales has been expanded further east across southern England.

It comes as the UK continues to swelter in the grip of a heatwave that is expected to last for several more days.

The Met Office said the heavy rain could lead to flooded homes and businesses and difficult driving conditions.

Forecasters said: "Some 30mm-40mm of rain in an hour is possible.


Image: The warning has been extended across more of southern England

"Where surface water flooding or lightning impacts do occur they are likely to be in only a few places rather than across the whole warning area.

"The greatest chance of impacts is in the afternoon, with the risk decreasing again on Sunday evening."

About a week ago, the Met Office announced that it was bringing in two new types of weather warnings - one for thunderstorms and the other for lightning.

Lolly good fun! Animals fight to keep cool

This is the first time the thunderstorm alert has been officially put out.

Sky News weather producer Joanna Robinson said: "There's finally some rain over the UK, but it's confined to southwestern parts.

"It will be welcome rain for gardeners and farmers, but torrential downpours will bring the risk of local flooding.

"The Hebrides and northwest Ireland may see a little rain on Sunday too, but most other places will be fine again.

"Looking further ahead, computer models suggest no widespread rain for the first half of July, increasing the drought and wildfire risk.

"There'll be just a few thunderstorms around at times.

"If you're caught up in the rain today, you may notice a pleasant earthy smell as the rain falls. This is called petrichor."

Meanwhile, despite the weather warning, millions of customers are being asked to conserve water supplies by not using hosepipes or water sprinklers.

The hot spell has put a strain on utility companies, which have been pumping millions of extra litres into their systems.

The first hosepipe ban began in Northern Ireland at 6pm on Friday, and Severn Trent Water, which is based in the Midlands, has asked people to be "careful with their water".

Image: The high temperatures have caused some rail tracks to buckle

Severn Trent, which has almost eight million customers, said: "We're set for another hot weekend, and, with demand for water really high, we're producing millions of extra litres.

"We're asking customers to be careful with their water and for now avoid using the garden sprinkler or hosepipe."

The company has issued tips on conserving water including:

:: Put garden sprinklers away - a sprinkler can use as much as 1,000 litres of drinking water in just one hour, which is more water than a family of four would normally use in a whole day.

:: Take a shower rather than a bath. It uses 40 litres less water and it's quicker.

:: Use a bucket and sponge rather than a hose. If you clean your car for 30 minutes you'll use 50 times less water with a bucket instead of a hose.

Image: The UK has been sizzling in a heatwave

The UK had its hottest day of the year so far on Thursday, with the mercury hitting a high of 33C (91.4F) in Porthmadog in northwest Wales.

Highs of 30C-31C (86F-87.8F) are expected today, with the mercury having hit 29.5C (85F) on Saturday.

Sky's weather producer Joanna Robinson said: "Southwest Britain will be at risk of thunderstorms today as humidity increases in the South.

"Any rain there will be welcome to gardeners and farmers, but torrential downpours could lead to some local flooding.

"The storms will be hit and miss, with parts of the southwest staying dry."

Image: People enjoy lunch in the sunshine near Tower Bridge in London

Next week, most areas are expected to stay dry, with no significant rain forecast.

There will be plenty of strong sunshine again, with temperatures remaining well above the average.

Meanwhile, growers have warned that the heatwave could lead to lettuce shortages on supermarket shelves.

The warm weather has seen demand rising for the salad vegetable, but with temperatures above 30C (86F), lettuce crops have stopped growing.