The reading was taken at Cambridge’s University Botanic Garden.
The previous record was 38.5C, recorded at Faversham, Kent, in August 2003.
Dr Mark McCarthy from the National Climate Centre (NCIC) at the Met Office said: “As the official source of meteorological statistics for the UK, we take the quality of our recordings very seriously.
We are talking about a potential new record for the highest temperature recorded in the UK and we therefore need to thoroughly investigate the observation with our partners at Cambridge University Botanic Garden through statistical analysis and by visiting, to check the site and equipment and ensure there are no potential problems.”
The UK has been in the grip of a heatwave for the entire week, with high temperatures yesterday causing travel chaos.
Cops had to be called to a lido in south London after more than 500 people tried to storm the pool, causing it to shut its doors for the day.
Temperatures today are cooler and Brits have already seen rain, with the country set to cool down over the next few days.