The warm, dry weather was predicted to continue for one more day after firefighters tackled a series of blazes across Britain during record-breaking temperatures.
“Wall-to-wall sunshine” was expected on Wednesday before the return of showers and milder temperatures, according to forecasters.
February’s exceptional conditions have seen fires at Arthur’s Seat in Edinburgh, on West Yorkshire’s Saddleworth Moor and in North Wales, Sussex and Lancashire.
Firefighters may welcome the showers that are predicted for much of the UK on Thursday, while those enjoying unseasonable sunbathing may not.
Met Office forecaster Dean Hall said temperatures as high as 20C (68F) could be recorded in London on Wednesday, with largely “wall-to-wall sunshine across the UK”.
“It’s going to feel pretty pleasant out there so certainly make the most of this exceptionally mild weather,” he said.
But he added: “Today is going to be the last day of any warmth and dry, settled weather.”
Cloud is predicted to move in and bring with it rain across much of the UK, while Scotland may be spared.
“Some of those showers could be heavy and there could be a rumbling of thunder with that as well,” Mr Hall said.
The UK saw a new winter record temperatures set in two consecutive days, with a reading of 21.2C (70.2F) at Kew Gardens in London.
Experts said climate change is heating up the whole weather system and making extremes more likely.
Mr Hall added that the impending downpours may “mitigate” the dry conditions faced by firefighters.
Crews were expected to bring the blaze at Arthur’s Seat under control, while firefighters believed they had quelled the one on Saddleworth Moor.
A man was rescued from a tractor in Glyndyfrdwy in North Wales after a nearby blaze, which firefighters were continuing to tackle on Wednesday morning.
Flames were extinguished in East Sussex’s Ashdown Forest, which was made famous by the Winnie-the-Pooh books, and on moorland in Blacko, Lancashire.
A series of gorse fires were also out on The Lizard in Cornwall, with firefighters saying the majority were suspected arson.
Wet and windy conditions are predicted for the weekend.