Londoners were flocking to parks and lidos on Tuesday as a mini-heatwave hit the capital.
As warm weather has been forecast, the Met Office has issued a stark warning about thunderstorms and lightning which could increase the risk of flooding and power cuts in the South West and Wales from Wednesday.
Temperatures are expected to soar to 29C in parts in London as the country enjoys a warm start to September.
The glorious sunshine - which follows weeks of rain and unsettled conditions – will last until the end of the week before giving way to cooler temperatures and a risk of some heavy showers, forecasters said.
Across the UK temperatures are forecast to reach up to 30C on Tuesday.
The Met Office said some areas were edging close to recording an official heatwave this week as pupils head back to school.
On Monday, the maximum UK temperature was logged at 28.9C in Larkhill, Wiltshire closely followed by the 28.8C recorded at Santon Downham, Suffolk and 28.7C at Middle Wallop in Hampshire.
In Wales, the highest temperature was 27.1C at Usk in Monmouthshire while the mercury reached 24C at Fyvie Castle in Scotland’s Aberdeenshire and 22.2C at Ballywatticock in Northern Ireland.
Greg Dewhurst, a Met Office meteorologist, said central and eastern England were the likely areas that could experience a maximum of 30C on Tuesday. London is expected to reach at least 29C.
More widely across England and Wales, conditions will be in the mid-to-high 20s, while Scotland and Northern Ireland could see temperatures around 24C to 25C.
Mr Dewhurst said low pressure moving in from the south west on Wednesday make it “less hot” in parts of Wales and Northern Ireland, but “hot air” will remain in central and eastern England and Scotland, bringing highs of 26C to 29C.
Temperatures will fall later in the week, with an increased risk of some heavy showers.
Mr Dewhurst said central and eastern parts of England were “most likely” to record an official heatwave across Monday to Wednesday but will only “just about make it”.
“We often get a warmer spell particularly early on in September,” Mr Dewhurst said.
He added: “August was particularly cool… and cloudy, so this spell is the warmest spell of weather since July for the UK.”
September has already beaten this August’s highest temperature of 27.2C in the UK, which last happened in 2016.
But the warm weather isn’t here to stay.
Stormy weather could be on the cards from Thursday as the Met Office warned about heavy showers for the north and southwest of England and Midlands from 11am to 8pm on Thursday.
Torrential downpours could dump 30-50mm of rain fall in less than three hours in some parts of the country on Wednesday and up to 40mm in two hours on Thursday.