Glastonbury is expected to be a gloopy mud-fest and Wimbledon a wash-out with week-long heavy rain predicted from June 24, according to weather experts.
Scorching temperatures of up to 32C could hit Britain this month but will only break up week-long rain spells, according to a dismal summer forecast.
But forecasters said highs up to 33C are due from late July as school holidays start, with hot air from Africa expected - but summer’s hot periods are forecast to be short, with no long heatwaves.
This week is set to be mixed, with sunny spells to Thursday as highs rise from 19C on Monday to around 21C by midweek before thunderstorms potentially return.
A sunny weekend saw Sainsbury’s sausage, BBQ and picnic food sales quadruple.
Tesco projected weekend sales of a million sausages, 1.5 million ice cream cartons and 25 million cans of beer and cider while 150,000 horse-racing fans basked at Saturday's Derby at Epsom.
But rain threatens the Isle of Wight music festival, starting on Thursday, and the Download music festival, starting on Friday at Donnington Park.
Met Office forecaster Charlie Powell said: "I think the warm weather will last certainly for the next couple of days.
"We've got high pressure building its way from the west and that will hang around certainly for the next few days.
"By Thursday we might start to see a bit more rain starting to make its way in from the north or the south, or both.
"Although temperatures will be up, it may be accompanied by some sharp and maybe thundery showers across the southern third of the UK."
WSI Europe meteorologist Mark Stephens-Row said: "We expect June, July and August to all be warmer than average - with highs up to 33C expected, most likely in late July and early August, meaning good news for school holidays.
"Hot air will push to the UK from north Africa and Madeira.
"But we're not forecasting heatwaves for weeks like 2003 and 2006.
"We expect week-long periods of un-summerlike wet weather."
Most of the UK basked in glorious sunshine this weekend, with up to 26C in some areas on Friday - the hottest this year, although there were also heavy showers elsewhere and nearly 5,000 lightening strikes.
Thermometers hit 26.7C in Frittenden in Kent, beating the previous 2015 high at nearby Faversham on April 15.
But inch-wide hail and a week's worth of rain in one hour also hit some places, despite the balmy conditions.
Originally published on the Mirror Online.