The confirmation comes after quality control testing was carried out at a number of sites where records were provisionally broken during the extreme heat, the Met Office said.
A new record for Wales of 37.1C at Hawarden Airport, Flintshire, on July 18, was also confirmed, as was a new record high daily minimum temperature for the country, of 24.5C at Aberporth on July 19.
But a provisional record for Scotland of 35.1C, reported at Floors Castle, in the Borders, does not meet the criteria needed to be declared an official national record, the Met Office said.
An inspection found the site set-up was not fully compliant with observing standards.
A new record for Scotland of 34.8C at Charterhall, in the Borders, on July 19 was confirmed.
The confirmation of the provisional records comes following measures to double check, including physical inspections, cross-checking of stations and sites and further testing of equipment.
The extreme temperatures were recorded as the UK was hit by an unprecedented heatwave, in which the previous UK temperature record of 38.7C was provisionally met or exceeded at 46 stations, from Kent to North Yorkshire and from Suffolk to Warwickshire.
Verification of these records has confirmed the extreme heat that we experienced last week
Ali Price, Met Office
Provisionally, seven stations recorded maximum temperatures in excess of 40C.
Ali Price, whose team is responsible for operating the Met Office network of weather observing stations in the UK, said: “Verification of these records has confirmed the extreme heat that we experienced last week.
“The process of verifying these records, using a rigorous process to ensure the readings collected were accurate, is vital to ensure that our temperature records reflect our weather and climate and have not been adversely influenced by other factors.”
Official temperatures come from weather stations that meet specific criteria, and are regularly maintained and inspected by specialist teams, the Met Office said.
They have thermometers housed in a white slatted box with its door facing north, to keep the thermometer away from direct sunlight but with constant airflow, to ensure consistency of readings.
The location of the boxes, known as a Stevenson screen, are also standardised, and have to be mounted 1.25m over level grass ground, and at least 20m away from concrete or hard-standing.
Only half the area within a 100m radius should be formed of man-made surfaces.
In a climate unaffected by human-induced climate change, it would be virtually impossible for temperatures in the UK to reach 40C
Mark McCarthy, Met Office
Dr Mark McCarthy, of the National Climate Information Centre, said: “Verification of these record-breaking temperatures confirms what we’ve been saying in the last week, that the UK exceeded 40C for the first time as part of a widespread and intense heatwave.
“In a climate unaffected by human-induced climate change, it would be virtually impossible for temperatures in the UK to reach 40C but climate change is already making UK heatwaves more frequent, intense and long-lasting.”
Quality control for a provisional new UK highest daily minimum temperature record – which represents the warmest night recorded in the country – continues.