The UK’s hottest day of the year so far – and the warmest September day since 1911 – has been recorded in Gravesend, Kent, where it reached 34.4C (93.9F).
The spell of warm Autumn weather is forecast to continue across parts of England until Friday.
Public Health England (PHE) and NHS England have both warned that the weather can pose a risk to health.
Elsewhere, there has been heavy rain and thunderstorms in parts of northern England and on the south coast.
A yellow warning for rain is in place for northern England, as well as for southern Scotland.
As much as 30mm (one inch) of thundery, torrential rain could cause flash flooding and travel disruption, the Met Office said.
Prestbury in Cheshire had 32.4mm of rain in an hour, the Met Office said, while Manchester City’s Champions League clash with Borussia Monchengladbach has been postponed – with pictures showing huge amounts of water on the pitch.
The highest temperature of 2016 had previously been 34.1C, which was reached on 23 August at Faversham in Kent.
The all-time record for September of 35.6C (96.1F) was set in 1906, in Bawtry, South Yorkshire.
NHS England has declared a level-two heat alert, which means there is a high chance that an average temperature of 30C (86F) by day and 15C (59F) overnight will occur over the next two to three days.
These temperatures can have a “significant effect” on a person’s health if they last for at least two days and the night in between, it said.
Dr Thomas Waite, from the extreme events team at PHE, said: “Think today about what you can do, and for those around you, to stay cool during the daytime and particularly at night.
“Much of the advice on beating the heat is common sense and for most people there’s nothing to really worry about.
“But for some people, such as older people, those with underlying health conditions and those with young children, summer heat can bring real health risks.”
Meanwhile, meteorologist Mark Wilson said there had been “a lot of rain in a very short space of time” in north-west England, along with “a lot” of thunder and lightning.
“There are some torrential downpours passing through parts of the country at the moment but they will ease,” he said.
The forecaster said the band of rain and thunderstorms looked set to push eastwards into Yorkshire and up to Scotland over the course of the night.
Manchester Airport tweeted that some inbound flights had been affected because of the storm, but later added that it was “fully operational again”. (BBC News)