A new June provisional record temperature of 37.7C was recorded in Lingwood, Norfolk, on Friday, beating the 37.3C recorded at Santon Downham in Suffolk on the same day, the Met Office has revealed.
That, in turn, surpassed the high of 36.7C recorded in Merryfield, Somerset, on Thursday.
Subject to verification, the 37.3C high would be a new record for the UK.
It would beat the previous June record of 35.6C, set in 1976, by more than 2C.
That is significant as such records have usually been broken by only a fraction of a degree in the past.
Much of Britain was engulfed by the heatwave for several days last week, with some public transport halted and public attractions closed due to the soaring temperatures.
A hosepipe ban was also brought in in Kent amid surging demand for water.
Scientists warned on Friday that the heatwave would have been virtually impossible 50 years ago.
They said that human-driven climate change is fuelling more intense and frequent extreme heat events.
There were at least 571 schools either fully or partially closed because of the heat, including in Somerset, Gloucestershire, Herefordshire, Buckinghamshire, Oxfordshire, West Berks and Worcestershire.
Several hospitals declared critical incidents, with University Hospital Southampton being forced to cancel a number of planned operations and some outpatient appointments.
Health chiefs warned of the impact the conditions were having on services as they faced significantly more life-threatening emergency calls.
Met Office chief forecaster Andy Page said: “This exceptional heat has been unprecedented for June and is another marker on how climate change is shifting the dial on temperature extremes in the UK.”
Eurostar cancelled several of its trains between London and Paris on Friday evening “due to an exceptional spell of extreme heat” on its network.
Sheffield’s tram network was also suspended on Friday afternoon because of the extreme heat.
The AA said that its patrols had recorded almost one third (30 per cent) more breakdowns than on a normal Friday, adding that the heat was “taking its toll, particularly on older vehicles and those that haven’t been serviced”.
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