What temperature records could be broken?
The mercury could reach 38.5C, the highest temperature ever recorded in the UK.
Here are some of the key temperatures that could be matched or surpassed before the weekend:
33.3C: highest temperature recorded so far this year, on July 23 at Santon Downham in Suffolk
34.5C: highest recorded last year, on June 21 at Heathrow airport
35.6C: highest recorded in 1976, on June 28 in Southampton
36.7C: highest July temperature on record, set on July 1 2015 at Heathrow airport
38.5C: highest temperature ever recorded in the UK, set on August 10 2003 at Faversham in Kent