The UK has recorded its warmest temperature of the year so far, with Northolt in west London hitting 28.3C (82.9F) on Wednesday.
It is the third day this week that the record for hottest temperature of 2021 has been broken, after Kinloss in northern Scotland hit 24.6C (76.3F) on Monday and Cardiff recording 26.1C (79F) on Tuesday.
On Wednesday, parts of Surrey and Kent saw temperatures of between 27C (80.6F) and 28C (82.4), while the Met Office said Wales and Scotland had their hottest days of the year so far, with Hawarden in Wales recording 26.5C (79.7F) and temperatures in Achnagart, Scotland, reaching 25.4C (77.7F).
Northern Ireland matched its previous warmest day of the year, with 23.3C (73.9F) recorded in Ballywatticock.
Despite the scorching temperatures, parts of southwest England and South Wales saw some heavy showers in the afternoon.
The rain is likely to move northwards into the evening with heavy and potentially thundery showers expected, the Met Office said.
However, despite the expected rain Met Office meteorologist Greg Dewhurst said the rest of the week would still be "on the warm side" – even if temperatures decrease slightly on Thursday.
"Temperatures on Thursday are expected to be around 26 to 27C across southeast England and East Anglia," he said. "And then through the rest of the week we’ll generally see a mixture of sunny spells and a few showers, and temperatures around 24 to 25C.
"So it’s not quite as hot for the rest of the week compared to the maximum temperatures on Wednesday, but still staying above average for this time of year."
With the summer just beginning there is still plenty of time for temperatures to climb further and possibly approach the 2020 high – when 37.8C (100F) was recorded at Heathrow on 31 July.
The latest warm conditions follow a wet and cold May, which was the fourth wettest on record for the UK and the wettest ever for Wales.
And the UK could see further glimpses of that on Friday, with thundery rain forecast in the South East.
The Met Office said the conditions will be mixed next week, with a good deal of dry weather mixed with outbreaks of rain in some parts.