The UK Met Office has said the temperature at Heathrow in west London has reached 33.5C, "provisionally beating the all-time May record".
It comes after the UK saw its hottest May day for at least 79 years yesterday with a high of 32.3C at Kew Gardens in southwest London.
Met Office meteorologist Tom Morgan said: "We rarely see temperatures above 35C, even in the summer months, so to see temperatures getting close to 35C in May is, as I say, pretty historic."
Wales also reached 2026 record temperatures of 27.4C in Cardiff yesterday.
Scotland saw highs of 23.5C in Edinburgh yesterday, just below the current record of 23.6C recorded in Aboyne on 1 May.
The Met Office said heatwave conditions were met in eight parts of England yesterday - Heathrow in Greater London, Benson in Oxfordshire, Brooms Barn in Suffolk, High Beech in Essex, Kew Gardens in London, Northolt in London, Santon Downham in Suffolk and Writtle in Essex.
Although today is set to be hot for many parts of England, northwest Scotland will be breezier and damper with thicker clouds.
The UK Health Security Agency (UKHSA) issued its first amber health alert of 2026 on Friday, warning that there is a risk of a significant impact across health and social care services. The alert will remain in place until Wednesday.
The heat is considered to be dangerous for some vulnerable groups including older adults as their bodies struggle to regulate temperature.
Age UK recommends staying inside during the hottest hours of the day, between 11am and 3pm, and having regular cold baths or showers.
Age UK charity director Caroline Abrahams said: "We can all help older people stay safe during periods of hot weather by checking in on older relatives, friends and neighbours to see if they need anything or are struggling with the heat.
"Offering to pick up shopping or medication, or even lending a fan, can make a real difference."
Read More: Record temperature for single day in May could be broken - Met Éireann
