As Britons swelter under yet another heat wave, forecasters are warning that a brutal summer is on course to become the hottest yet.

The Met Office, Britain’s weather agency, issued an amber warning — the second highest level — for Thursday in large parts of southeast England.

The extreme heat has remade summer for a country where many once escaped abroad to feel the blazing sun on their skins.

“An English summer is not the same anymore,” said Jacqui Browne, 67, as she sat on the brown grass of a London park.

On Thursday, temperatures in London are expected to reach 37 degrees Celsius (98.6 degrees Fahrenheit), according to a forecast by the Met Office.

There was a time when British summers were more temperate and marked by rain, but drought conditions have left large parts of the country parched.

The north, for example, is not as cool or green as usual, said Ms. Browne’s sister Janice Kennedy, 66, who was visiting from there.

“Even up north it’s quite warm,” Ms. Kennedy said. “Not like down here, but it’s quite warm up there, as well.”

Some, like Ms. Browne and Ms. Kennedy, still remember the summer of 1976, when repeated long spells of hot and dry weather made it the benchmark for hot summers. Now, that seems almost quaint.

The summer of 2022 stands out in memory for its intensity. It was then that Britain recorded a temperature above 40 degrees Celsius for the first time, according to the Met Office.

“Now it’s been overshadowed by the last three or four years,” Ms. Browne said.

By the end of this past July, Britain had already recorded 37 days of extreme heat, nearing a record set in 1995, when 39 days were recorded, according to figures from the weather agency.

Even if the last weeks of August are slightly cooler, the weather is still likely to break existing records, according to Met Office predictions.

“Another record-breaking summer now looks increasingly likely for the U.K., following the second-warmest June and second-warmest July on record, and yet another heat wave imminent,” Mike Kendon, the Met Office’s senior scientist, said in a statement this week.

“These statistics are a clear reminder — if one were needed — of the stark changes that we are seeing in the U.K.’s climate,” Mr. Kendon said.

The heat has persuaded some to rethink how they spend their summers.

“I think you might find that is a real win for coastal towns,” Mike Jones, 55, said as he and friends cooled off in a London park. “I think there’ll be more staycations, too.”

His friend Caroline John noted a downside.

“When you go abroad, you have a cocktail and the sea,” she said. “Whereas, in London, you’re on the tube in the heat.”

The sweltering subway system is just one example of a region not built for heat, both agreed. Train lines have buckled in the heat, causing many delays over the summer.

“We’re not equipped, are we?” Ms. John, 50, said.

Britain’s weather agency warned that Thursday’s temperatures could affect heat-sensitive infrastructure in homes and businesses. And delays on the road and rail were expected, with potential health and welfare concerns for those stuck on the road.

The high temperatures could also lead to health complications for some, especially older people and those with vulnerabilities.

But for Anesta Logan, 61, who was in the park with Mr. Jones and Ms. John, the new British summer is an improvement over the cool ones she grew up with, to say nothing of the freezing winters.

“The hotter, the better,” she said. “People are always going to complain.”