A new yellow warning has been issued by the Met Office for heavy showers and thunderstorms, while festivalgoers are set to be hit by more wet weather.
The warning stretches from south-west England and parts of Wales across the Midlands to the east of England, and will be in force from midday until 9pm on Saturday.
It means flooding of a few homes and businesses is likely, trains could be delayed and car journeys could take longer, the forecaster said.
Some areas within the warning could see 15-25mm of rain in an hour, and 30mm in two to three hours, along with hail and lightning.
Meanwhile, people at Reading, Leeds and other live music events are likely to see rain on Saturday as low pressure pushes eastwards, which will be followed by heavy showers.
The cricket is likely to be affected by showers at Lord’s in London, the Met Office added.
Four areas, mainly across the Midlands, are covered by Environment Agency flood alerts, meaning floods are possible.
It comes after continued hot weather across the UK, which coincided with extremely dry conditions.
The Met Office has previously said the UK is on course for its hottest summer on record after five heatwaves, with temperatures of up to 38.1C recorded in London.
Festivalgoers at Reading Festival were pictured frolicking in the rain during the event on Friday, with many laughing and posing for photos as they remained in good spirits despite their outfits being drenched in mud.
While some were seen flinging mud at each other and playing in puddles, others were hiding beneath their plastic ponchos as they braved the poor weather conditions.
Geese frontman Cameron Winter warned festivalgoers not to “drink the water” on Friday as heavy rainfall seeped through the tent during their set.
Met Office meteorologist Greg Dewhurst said: “An area of low pressure is currently pushing eastwards across England and Wales and Northern Ireland, pushing rain across the country. That’s going to be followed by heavy showers.
“Temperatures generally reaching the low 20s, highs of 22-23C.
“It will be a different picture for Scotland even though it’s largely cloudy, there will be some brighter spells.
“For most it’s quite a bright start tomorrow, but it won’t be long before showers bubble up.
“We will see heavy showers developing throughout the day in the north and west of the UK and some thundery weather.
“With tomorrow being a bit more of a day of sunshine and showers, it should mean with a bit more sunshine around temperatures will be a bit higher, with highs of 20-23C for most and isolated areas could see 24C.
“Monday will be a brighter day for most, quite a lot of cloud around, but also showers, more frequent in the north of the UK. Temperatures may come down a touch, between 19-22C, maybe locally 23C.”
And wind gusts of 35-40mph could be seen on the south coast on Saturday, while Leeds Festival could get some gusty winds on Sunday if heavier showers hit.
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