Sizzling Britain is expected to record the hottest temperatures of the year, with the prospect of the mercury rising even higher on Sunday.
The heatwave is forecast to continue into next week.
Forecasters said highs of 27C (80F) were measured in pockets of England early on Saturday afternoon, a shade off the year's record: 27.2C at Heathrow on June 30.
Updated figures later are expected to eclipse that, with up to 30C (86F) expected in parts of southern England.
The weather will be much hotter than usual for the time of year - the average maximum temperature for July in England is 20.9C (69.5F) - and many parts of the country will enjoy temperatures on par with popular Spanish holiday resorts, forecasters said.
Tom Tobler, a forecaster with MeteoGroup, the weather division of the Press Association, said several areas have recorded highs of 27C.
"Parts of London have seen 27C, while the east Midlands, Yorkshire and East Anglia have all been past the mid-20s," he said. "We haven't had the best of it yet. It could be even warmer later on today, while tomorrow could be the best day of this spell."
Most of the UK has experienced widespread sunshine, although people in parts of northern Scotland were left clutching their umbrellas under rain and drizzle.
Mr Tobler said: "Tomorrow will be around 30C, if not 30C, and there is potential for it to be the hottest day of the year. The high pressure is just staying in place for the next week or so at least. Tomorrow might well be the warmest of that period."
The last time the country enjoyed a long spell of warm July weather was in 2006 when temperatures were above 28C (82.4F) in many areas for a fortnight. More recently, temperatures peaked at 30.7C (87F) between July 23 and 26 last year. The previous highest temperature of the year was 27C (80F) on June 30 but recent years have seen Britons endure wet and overcast summers.