The previous hottest May day saw 32.8C heat, first registered in 1922 and again in 1944.
It is just the latest temperature record to tumble in the UK, which saw its hottest year on the books in 2025, with scientists warning that the country is unprepared for the ever-more frequent heatwaves driven by man-made climate change.
The Met Office had earlier forecast highs of 35C, after heatwave conditions spread to parts of southeast England and London by Sunday night.
“Temperatures at Heathrow have recently reached 33.5C, provisionally beating the all-time May record,” the Met Office wrote on social media.
“Records are usually only broken by tenths of a degree – making this heatwave unprecedented for the time of year,” the weather agency added earlier.
Climate advisers last week warned the UK government that the country was “built for a climate that no longer exists” and urged it to adapt infrastructure like schools and hospitals for a warming planet.
Scientists say human-induced climate change is making extreme weather events like heatwaves, droughts and floods more intense, resulting in temperature records being broken more frequently.
The national weather service in France also said the country has faced unusually hot weather.
Paris on Saturday notched up its first temperature above 30C of the year, hitting 31.9C. (AFP)
