Will today be the hottest day of the year? Met Office forecast for Thursday

And the mercury could reach 30C - the earliest point on record that this temperature has been reached.

Met Office meteorologist Michael Silverstone says temperatures could climb to “29C or even 30C”.

He added: “If we reach 30C on Thursday, it will be the earliest date in May that the UK has seen 30C since our records began in 1860.”

The Met Office said temperatures reached 26.7C in Wisley, Surrey on Wednesday – making it the warmest day of the year so far. The previous high was 24.5C in St James’s Park, London, on Monday, which reached 24.7C on Tuesday.

Despite the soaring temperatures, the Met Office has ruled out a heatwave this week. Mr Silverstone said it looks “unlikely” the UK will reach a heatwave – which is defined as three consecutive days of temperatures exceeding the “heatwave threshold”, which varies across the country.

The threshold is 25C for most of the UK, rising to 28C in London.

“Admittedly, it could be close for a few places in the south, though, with temperatures either today or Friday only just failing to exceed the required threshold,” Mr Silverstone said.

The warm weather could also challenge the record for the highest April temperature in Wales, which is 26.2C.

But temperatures are expected to ease by Friday, and Saturday will bring cooler conditions of 14C to 18C across the UK.

The London Fire Brigade (LFB) has urged caution around open-water swimming after a 32% increase in water-related incidents last month compared with the same period last year.

Craig Carter, LFB assistant commissioner for prevention and protection, said: “Even when the sun is shining, water temperatures can be dangerously cold. Cold water shock can affect anyone, no matter how fit or experienced they are. It can lead to water inhalation and, in the worst cases, drowning. Be particularly careful near the water’s edge, it’s easy to slip and fall unexpectedly. And think twice before jumping into open water.”