It's happened several times:
From the brilliant Trevor Harley's site:
https://www.trevorharley.com/hottest-day-of-each-year-from-1875.html
1922 32.8 Camden Square 22 May
1944 32.8 Tunbridge Wells, Horsham, London (Camden Square and Regents Park) 29 May
1965 29.4 Camden Square London 14 May
(And what I wouldn't give to see a year like 1965 - can you imagine, not even getting to 30C?)
Originally Posted by: Retron