A yellow heat health alert has been extended to all regions in England. Temperatures are set to reach 31C on Thursday and are expected to climb as the third heatwave of the summer hits the UK. The highest temperatures are forecast for Saturday, with England and Wales expected to deal with the hottest weather. This will make for a sweltering start to the finals weekend for Wimbledon fans and players taking to the courts in SW19.

Scotland is also due to hit the heatwave threshold, according to the Met Office, whereby the temperature needs to reach or surpass 28C in the south and 25C in the north for at least three consecutive days. Despite not being as warm as the heatwave at the beginning of July, the hot spell is forecast to last longer and cover a broader area, according to the forecasting body.

The UK Health Security Agency issued yellow heat health alerts on Wednesday covering parts of central and southern England, valid until 10am on July 15, with the body extending the warning to cover all regions in England from 11am on Thursday.

According to the Met Office, temperatures are expected to reach 27-29C widely across England and Wales on Thursday afternoon, with isolated spots in the West Country and London area potentially seeing highs of 31C.

There is a "low probability" of reaching 32C, the forecasting body added.

Met Office meteorologist Alex Deakin said: "It'll be a sunnier day on Thursday compared to Wednesday. Some mist and low cloud possible in around the Irish Sea as well. That may affect the east coast of Northern Ireland, the south-west of Scotland and the Isle of Man at times, but again, most places will be sunnier than today across England, Wales, Southern Scotland, Northern Ireland.

"There will be this chain of thicker cloud, rain and drizzle at times across the far north of the mainland of Scotland, the Northern Isles, and the Western Isles where as a result, as you might imagine, it will again be on the coolish side with temperatures a touch below average, perhaps in the mid-teens.

"But elsewhere, we'll be ticking those temperatures up once more, particularly across England and Wales. First day likely to get over 30C, but it won't be the last day this week.

"All thanks to an area of high pressure squashing the air and the combination of that and the sunshine this time of year will allow those temperatures to continue to rise into the weekend.

"So, the hot conditions are going to last through the weekend."

Friday is expected to be hotter than Thursday, with temperatures reaching 27C across the north and 32C further south and south east.

Saturday is set to be the hottest day of the week, with London potentially reaching 33C and high UV and pollen counts across much of the country, before a similarly hot day on Sunday with temperatures forecast between 27 and 31C.

"Prepare for some hot conditions as a heatwave returns to the UK," Met Office meteorologist Clare Nasir said.

Ms Nasir advised people to "stay hydrated", echoing warnings from the Royal Society for the Prevention of Accidents (RoSPA) which urged the public to drink water regularly, seek shade and use sunscreen.

Steve Cole, policy director at RoSPA, said: "Heat is no longer just a holiday perk - it's a growing public health risk. We're seeing more frequent and intense heatwaves, both in the UK and globally, and the data shows a clear rise in heat-related illness and fatalities.

"Warm weather can also be deceptive when it comes to going for a dip. While the air may feel hot, water temperatures often remain dangerously cold, which can lead to cold water shock, even in summer."

People are also urged to take extra care when it comes to barbecues in the heat.

Leigh Hamilton, ranger service manager at Loch Lomond & The Trossachs National Park Authority, said: "May's wildfire at Glen Finglas, caused by a carelessly discarded disposable barbecue, is a stark reminder as to the devastating impact a single reckless act can have on our National Park.

"This summer, as we face continued drier, more fire-prone conditions, we urge everyone to be vigilant and act responsibly, especially during high-risk periods. Avoid naked flames including disposable barbecues, dispose of waste properly, and call 999 immediately if you witness a wildfire.

"Everyone has a part to play. If you care about this landscape, help us protect it."