The UK was hotter than parts of Hawaii on Sunday as sweltering temperatures soared to just below 30C.
Ireland also recorded its warmest day of 2022 to date, with 25.6C reached at Shannon Airport in Co Clare.
The hot weather is expected to continue into next week, with UK temperatures set to soar above 32C on Monday and further on Tuesday, potentially making it the warmest day of the year so far.
The UK’s record high for 2022 currently stands at 32.7C, taken at Heathrow on June 17.
By 5pm on Sunday, Wisley in Surrey hit 29.5C, with temperatures in the high 20s across most of the country.
The mercury rose to year-high levels in Fife, with the Met Office recording 28.9C in the area just north of Edinburgh.
It meant parts of the country were warmer than areas along the US coast such as Los Angeles and parts of Hawaii, such as Maui.
Met Office forecaster Dan Stroud told the PA news agency: “It’s been very warm across England today, temperatures staying in the high 20s.
“Interestingly Scotland saw its hottest day of the year so far, while parts of Wales reached the mid-20s.
“Northern Ireland saw the coolest conditions, reaching highs of 23.4C, but most of the UK was still warmer than Mediterranean islands like Sardinia and parts of Turkey.
“It was pretty much wall-to-wall sunshine on Sunday, with a bit of cloud in Northern Ireland. but generally it was a very pleasant summer’s day.
“However, there’s a very uncomfortable night ahead for many, with temperatures remaining warm.”
A heat-health alert has been issued for some parts of the UK next week, with those in affected areas advised to shade or cover windows and check on the vulnerable and the elderly.
The mercury in London and the South East could hit 32C on Monday, Mr Stroud said.
The hot spell looks set to subside later in the week, when a cold front is expected to start pushing in.