Londoners have been advised to enjoy the hot weather while they can as temperatures are set to plummet by up to 10C.
A top temperature of 25C is forecast for the capital on Sunday, which would eclipse this year’s record of 22.1C for the whole of the south east.
But fortunes are set to change as weather will return to normal for spring time after a sunshine-filled Sunday, the Met Office says.
Forecaster Emma Boorman said: "From Monday onwards it's really all-change.
"The rain and cloud across the far north west is associated with a cold front.
"That will be making its way to the south east during Sunday night and introducing a much colder feel as we head into the start of the new working week.
"Temperatures in some places, for example, could be a solid 10 degrees cooler on Monday than they were on Sunday."
Sunseekers across the UK flocked to beaches and parks on Sunday as the temperature topped 25C in Cambridge, and rose to at least 20C in many parts of England and Wales.
Things to do in London in the hot weather
The summer-like weather saw the fire service called out to help an elderly woman who had to be cut free after becoming trapped in a sun lounger.
Devon and Somerset Fire and Rescue Service said they used cutters and bolt croppers to release the woman, who got her leg stuck in the incident at Barn Meads Road in Wellington.
She was given oxygen and the ambulance service was called.
While much of England and Wales enjoyed cloudless skies and warm weather all weekend, conditions became cooler on Sunday for Scotland and Northern Ireland, with highs of 16C (61F) and 15.2C (59F) respectively.
