The UK has experienced its warmest night on record, according to provisional Met Office figures.
Temperatures did not fall below 25°C in some places, experts said, which exceeded the previous highest daily minimum record of 23.9°C, recorded in Brighton on 3rd August 1990.
The record comes as forecasters predicted temperatures could exceed 40C for the first time on Tuesday in parts of Britain.
By midday on Tuesday the record for the hottest day in the UK had already been broken, with 40.2C recorded at Heathrow, beating the previous record of 38.1C.
Met Office forecaster Rachel Ayers had warned of a “difficult night of sleeping” before “a pretty unprecedented day” on Tuesday.
She said: “The temperature will be very hot throughout the day, before rising as high as 40C, maybe even 41C in isolated spots across England during the afternoon.”
The heat peaked at 38.1C in Santon Downham, Suffolk on Monday, making it the hottest day of the year and the third hottest day on record, after 38.7C in Cambridge in 2019 and 38.5C in Faversham, Kent, in August 2003.
Another record was broken in Wales, as a high of 37.1C was recorded in Hawarden, Flintshire, beating the previous record of 35.2°C, recorded at Hawarden Bridge, Flintshire on 2 August, 1990.
The mercury will sizzle at possible highs of 41C in isolated areas on Tuesday, making the country hotter than Jamaica, the Maldives and Barbados – with rail users warned of delays, cancellations and changes to train services.
Transport Secretary Grant Shapps has conceded the UK’s transport network cannot cope with the extreme heat.
As the heatwave continues, Shapps told people to “apply common sense” and “depending on the nature of your journey and reason for it, you might want to consider rearranging your day around it”.
He told BBC Breakfast: “We’ve seen a considerable amount of travel disruption. We’re probably going to see the hottest day ever in the UK recorded today, and infrastructure, much of it built in Victorian times, just wasn’t built to withstand this type of temperature – and it will be many years before we can replace infrastructure with the kind of infrastructure that could, because the temperatures are so extreme.”
Asked if the transport system can cope with the weather, he said: “The simple answer at the moment is no.
“Where those tracks are 40 degrees in the air, on the ground that could be 50, 60, 70 and more, so you get a severe danger of tracks buckling. What we can’t have is trains running over those and a terrible derailing.
“We’ve got to be very cautious and conscious of that, which is why there’s reduced speeds on large parts of the network.”