Members of the public cool their feet in the Princess Diana memorial fountain in London's Hyde Park on July 1, 2015. (Agence France-Presse)
The UK is experiencing its hottest day in nine years as temperatures reached 34.5C (94.1F) by midday and officials issued public health warnings over the elderly and very young.
By noon on Wednesday, Northolt in west London had overtaken Heathrow, with the airport proving a hot spot - both politically and physically - at 34.1C
As the mercury rose across Britain, an expected high of 36C was likely to see London hotter than Miami, LA and Rome, though Paris and Madrid were set to top the European league with predicted highs of 38C and 37C respectively.
As the Met Office weather map displayed a rainbow of purple (very, very hot), red (very hot) and orange (just hot) meteorologists were running out of metaphors and temperatures in Britain soared above those in Barcelona and Athens.
The hottest temperature on record for the month of July is 36.5C (97.7F) at Wisley, Surrey on 19 July 2006.
Public Health England (PHE) warned people to avoid the sun between 11am and 3pm, and to look out for the elderly, young children and those with serious illnesses. The message was to avoid physical exertion and drink plenty of water. Thunderstorms were likely in the south-west, spreading towards London later in the day.
Independent Age, a charity representing older people, called for vigilance and urged people to check on elderly neighbours who might suffer adverse effects and were vulnerable to heat stroke, heat exhaustion and dehydration.
By 9am, temperatures had reached 29.4C (85F) at Kew Gardens and at the Wimbledon tennis championships, extra water points were being laid on as capacity in the grounds was being reduced for a second day. Judy Murray - captain of the British Fed Cup team and the mother of professional tennis players Jamie and Andy Murray - joined calls for a "heat rule" for male players, bringing them into line with rules for female players.
Employers were urged to allow vulnerable workers to stagger their journeys to and from work to avoid overcrowded trains. Dr Angie Bone, head of extreme events at PHE, said: "During very hot weather, pregnant women and people who have chronic illnesses, including cardiovascular, respiratory, renal conditions, diabetes or Parkinson's disease may experience discomfort if indoor temperatures are particularly hot and in using public transport.
"Employers should ensure indoors areas are kept cool and consider allowing these individuals to travel to and from their place of work during cooler, or less busy times of the day."
Some wilting rail passengers were grateful for the free bottled water handed out on Greater Anglia trains at its major stations, including Ipswich and Norwich.
Lorry drivers, stuck in huge tailbacks on the M20 in Kent due to striking ferry workers closing the port of Calais, were also given water by coastguard teams. Kent county council was set to provide 5,000 bottles of water to drivers caught up in Operation Stack.
Transport looked likely to be affected, with Network Rail warning that metal rail tracks, which can get up to 20C (68F) hotter than the air temperature, could buckle. Speed restrictions would be put in place resulting in delays.
"We are maintaining track temperatures and if necessary putting in speed restrictions so we can protect vulnerable places and keep the trains moving," a spokesman said. "There will be delays, but they might not be significant delays."
Motoring group the AA warned roads could melt, causing disruption. The AA president, Edmund King, tweeted: "Some road surfaces can melt at 50C, so if weather hit 30s the ground temp can hit 50. You have been warned."
But relief is at hand. Temperatures are set to drop to 25C (77F) on Thursday with heavy showers in the evening - much more in line with a typical British summer.
The heatwave prompted fresh warning of the dangers of outdoor swimming after the body of a man was recovered from Alton Water reservoir in Tattingstone, Suffolk, on Tuesday evening.