“On August 10, 2003, the United Kingdom records its first-ever temperature over 100 degrees Fahrenheit.”
Temperatures in U.K. top 100 F for first time during European heat wave | August 10, 2003 | HISTORY
London reached 100F in 1911.
11 Aug 1911, 5 – The Guardian at Newspapers.com
It was 101.5 degrees in England in 1881.