The warmest temperatures anywhere in the UK fell on runners and spectators at this year's 34th London Marathon - as much-fancied crowd favourite Mo Farah came home in eighth place for his course debut.
Unbroken sunshine and barely a breath of wind meant the 11C (51.8F) recorded at the start of the race in Greenwich at 10am felt considerably warmer, as racers began the arduous 26.2-mile course through the capital.
More than 1,200 volunteers from St John Ambulance lined the streets as the mercury rose to 16C (60.8F)
Julian Mayes, senior forecaster with MeteoGroup, said: "It was a cool start, but things got much warmer.
"We have recorded temperatures of 16C in St James's Park (near the race finish line) - which is the equal highest anywhere in the UK today, along with London City Airport and parts of Kent.
"As we have seen over the last few days, the warmest place in the country has been London.
"That was very much the same today, and it was generally a good bit warmer in the capital than anywhere else.
"There was a bit of a breeze to begin with but that died down and the sun shone brightly, so runners will have felt it."
Medics advised runners to take on plenty of water and not to risk going for personal bests if the heat got too much, as the race got under way beneath virtually cloudless skies.
A huge cheer was reserved for Olympic hero Farah as announcers called out his name to the spectators as being among the ones to watch for.
But despite being installed among the bookies' favourites for the race, the 31-year-old failed to break into the podium positions,
Kenyan world record holder Wilson Kipsang took the Virgin Money London Marathon men's title in an unofficial time of 2hrs 04mins and 29secs, a course record, with Farah coming home almost four minutes back.
The Briton's time of 2hrs 08mins 21secs was outside Steve Jones' 29-year-old British record of 2:07:13 and could persuade him that his future remains on the track, rather than the road.
Champion runner Haile Gebrselassie had been recruited as pace-setter in an effort to encourage a record time - but forecasters said the heat may have had an influence on the race.
Race starters Katherine Grainger and Anna Watkins, who won the women's double sculls gold at the London 2012 Games, were two of 13 London Olympics gold medallists taking on the famous course, which ends at The Mall.
Kenya's Stanley Biwott was second in the men's race, with Ethiopian defending champion Tsegaye Kebede third.
Kenyan Edna Kiplagat won the women's elite race, ahead of compatriot Florence Kiplagat.
Kiplagat, the two-time reigning world champion, made up for the pain of finishing runner-up for the past two years in the capital to take the title in 2:20:21, with her namesake three seconds back.
There was disappointment for Britain's David "Weirwolf" Weir, who lost his bid to become the best wheelchair racer in the event's history.
He had been aiming to win his seventh title but was beaten into second place by Switzerland's Marcel Hug.
American Tatyana McFadden took the elite women's wheelchair race title, a month after winning a silver medal at the Winter Olympics for cross-country skiing.
Along every part of the course, the several-deep crowd cheered raucously as friends, colleagues and even strangers - with their names emblazoned across their vests - pounded the road.
Celebrities taking part included former Liverpool and England striker Michael Owen, Game of Thrones actress Natalie Dormer and Michelin-star chef Michel Roux Jr.
Labour politicians Ed Balls, Andy Burnham and Sadiq Khan also posed for "selfies" in their running vests in the moments before the race began.
And there was the customary collection of those undertaking the marathon in fancy dress - with plenty of comic book characters and furry animal costumes.
Another participant, serial fundraiser Tony Phoenix-Morrison, carried a 42kg fridge on his back.