Cambridge has recorded a temperature of 38.7 degrees, which if validated would be the hottest UK temperature on record.
The figure was captured at Cambridge University Botanic Gardens on Thursday, and forecasters said they will “investigate” the reading.
If proven it would outstrip the 38.5C recorded in Kent in 2003.
Met Office spokesman Dr Mark McCarthy said it takes its temperature readings “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 from Cambridge University Botanic Garden,” he said.
People queued to enter Cambridge's Lido on Thursday.
Officials have already confirmed a recording of 38.1C in Cambridge made Thursday the hottest July day on record, beating the previous high set at Heathrow in 2015.
Britons in the south-east sweltered through a stormy Thursday night, but a cool change has dropped temperatures to the mid 20s on Friday.
The Met Office said the weekend will see familiar conditions return, with an increased chance of rain for the east and north-east.
Others found themselves cooling off in the River Cam.
Health experts have warned hospitals to prepare for future heatwaves after a “totally unbearable” few days.
The Society for Acute Medicine president, Dr Nick Scriven, said the weather is “only going to become more extreme every year”.
“Tired and overheated staff are not capable of giving the best that their patients deserve and it is really time that hospitals and those running them took notice of environmental factors on top of all the existing stresses and strains,” he said.