Lord's relaxed its strict Pavilion dress code on Tuesday with members not required to wear jackets as temperatures soared into the mid 30s Celsius for the start of the County Championship game between Middlesex and Sussex.
Much of Britain is gripped in a heatwave with temperatures expected to threaten all-time records later on Tuesday, with predictions of the mercury rising above 40 degrees.
"MCC (Marylebone Cricket club) has advised us that the dress regulations in the Pavilion will be relaxed on Tuesday 19 July," a statement on the Middlesex County Cricket Club website said.
"Gentlemen in the Pavilion that day will not be required to wear a jacket, although MCC will still require Gentlemen to wear ties.
"Spectators should also adhere to the usual dress regulations on trousers and shoes."
It is not the first time hot weather has forced a relaxation of one of British sport's most traditional venues with the rules also being relaxed in 2018.
The stifling heat also led to two County Championship games between Gloucestershire and Hampshire and Northants and Lancashire having three reduced-length 90-minute sessions on Tuesday with play finishing at 1630 hours local time in the "interest of spectator and player welfare".
Several horse racing events have also been cancelled in Britain because of the heatwave.
