Britain has been basking in temperatures of up to 35.9C, falling just short of the all-time record.
Gravesend in Kent recorded the highest temperature of 35.9C, just 1.2C short of the national record hit in Cheltenham in 1990.
London reached 35.3C - the highest ever recorded in the capital - as the UK enjoyed the hottest day of the year so far.
The heat caused several train tracks to buckle - one prompting a train driver to stop his train as it approached Gatwick Airport. Overhead power cables were also damaged.
It also resulted in the London Eye being closed for about seven hours - reopening in the cool of the evening at 2030 BST - and in Berkshire police had to hand out water to motorists trapped in miles of tailback following a major crash.
Even Concorde was affected, with the supersonic airliner having to be diverted to Newfoundland for extra fuel on its way between London and New York - increasing the journey time by two hours - because of extra power needed on takeoff.
The justice system was also disrupted, with the heat forcing two trials to be adjourned.
A jury hearing an indecent assault case at Leicester Crown Court was sent home at 1500BST because the air conditioning could not cope.
In another court in the same building, jurors deliberating verdicts at the end of a three-month trial were sent home after sending a note to the judge, complaining of "intolerable conditions".
The London Eye was shut even though the temperature had not reached the maximum 30C inside the pods, a spokeswoman said. It was decided to close the popular tourist attraction "for the comfort of guests".
On the railways, Network Rail has said it will impose speed restrictions at noon each day, through to early evening, until temperatures drop below 30C.
Two buckled rails were reported on Tuesday and nine on Monday, it said.
Heat damage to overhead power cables near Shenfield in Essex also resulted in the closure of two lines out of Liverpool Street.
Passengers using the West Coast line were to be worst hit again on Wednesday, with 20 Virgin services cancelled between London, the West Midlands and Manchester, and other services altered.
Other cancellations included 17 First Great Western trains from London to Bristol and South Wales and five GNER London to Leeds services.
Long distance journeys between Scotland and the South coast were being diverted and similar disruptions are expected on Thursday.
A combination of cancellations, early terminations, extra stops, speed restrictions, and diversions are expected to affect many services across the country for the next few days.
On the roads, police officers were handing out water to motorists trapped in three miles of tailback following a major crash on the A34 in Berkshire, at the M4 Newbury junction.
"Officers have been tasked with attending a number of service stations and
supermarkets to get water for those who are stuck," a Thames Valley police spokeswoman said.
The weather has already claimed two lives in separate drowning incidents, both involving 17-year-old boys.
One died in when he went for a swim in a lake in Hurstbourne Priors, near Whitchurch, Hampshire. His body was discovered two hours after friends reported seeing the boy disappear below the surface, late on Tuesday afternoon.
The second tragedy happened at Aldwarke Lock in Rotherham, after a group of eight boys went for a swim on what was described as a "treacherous stretch of water" by South Yorkshire Police.
Neither victim has been named.
Electrical store Currys said it had sold 30,000 fans in the first three days of this week - a company record - as well as 100 electric blankets.
UK's hottest places
Gravesend, Kent 35.9
Wisley, Surrey 35.7C
Holbeach, Lincolnshire in 33.7
South Farnborough, Hampshire 33.4
However, not everybody was enjoying the heat, as thunderstorms in Northern Ireland left tens of thousands of homes without power overnight.
In North Belfast, a pensioner was in a stable condition in hospital after her home in Mount Vernon Lane was struck by lightning.
The Department of Health has issued "ten tips" for how people can stay safe in the high temperatures.
These include sitting in the shade or indoors, covering up or using sunscreen, drinking more water and less alcohol, ventilating your home and avoiding physical exertion.
Temperature extremes by continent:
Africa: 57.8C, El Azizia, Libya, 13 Sep 1922
Antarctica: 15.0C, Vanda Station, Scott Coast 5 Jan 1974
Asia: 53.9C, Tirat Tsvi, Israel, 21 June 1942
Australasia: 53.3C, Cloncurry, Queensland 16 Jan 1889
Europe: 50.0C, Seville, Spain, 4 August 1881
North America: 56.7C, Death Valley, California, 10 July 1913
Oceania (Pacific Rim): 42.2C, Tugnegareo, Philippines, 29 April 1912
South America: 48.9C, Rivadavia, Argentina, 11 Dec 1905
Source: BBC Weather Centre