People with plans for their three-day weekend will have to make the most of the the sunshine today before rain moves in tomorrow evening bringing what is set to be unpleasant weather on Bank Holiday Monday.
Top temperatures of 20C (68F) will feel much cooler as blustery showers and wind mar the last long weekend of the summer, the Met Office said.
The south west of the country will get the worst of the weather on Monday, with two bands of rain moving in, forecaster Kirk Waite said.
"The overnight rain will work its way through into Monday but then we have got another area of rain pushing across the south west into England and Wales," he said.
Ironically residents in Scotland, where it is not a Bank Holiday, will enjoy the best of the weather on Monday, with sunshine and little rain.
Today is set to be the best day of the weekend, Mr Waite said, with sunshine across most of the UK and just the odd shower on the eastern coast.
Cloud will edge in from the west on Sunday as places like Cornwall, where the Prime Minister is currently holidaying with his family, Devon and the west coast of Wales see the first of the rain.
While Monday has the "potential for brief interludes of drier weather", Mr Waite said it was likely to be a generally wet and windy day.
The unsettled weather is in strong contrast to the blistering hot August Britain enjoyed last summer, when temperatures reached 34.1C (88F).
The disappointing temperatures have prompted a last-minute rush for overseas holidays, the director of First Choice and Thompson reported, as Brits hope to catch more sunshine.
Andrew Flintham said: "This time of year is always popular for holidays, however with the predicted bad weather and the end of the summer of sport we're seeing more customers rush to squeeze in a last-minute break before the start of the new school year."
More than two million British holidaymakers are already booked to head overseas during the August Bank Holiday, travel association Abta said.
A spokesman for Abta said: "Typically, bad summer weather in the UK makes many people long for the sun and head off overseas.
"Next week temperatures in the UK are predicted to struggle to hit the high teens and the country will be covered by a bank of clouds, so many may be tempted to book a late break to the Mediterranean where temperatures will be in the 30s and hours of sunshine are guaranteed."
Back in Britain, 5.1 million people are planning an overnight holiday trip this weekend, VisitEngland said.
Meanwhile, around one million people are expected to be drawn to Notting Hill Carnival, Europe's biggest street carnival event, which will see hundreds of musicians and dancers join floats for a procession through west London tomorrow and Monday.