The phrase pushing the envelope arises from an East Anglian religious sect called the Broad Barringtons who broke away from Methodism in 1924 after a heated disagreement over the use of minor chords in hymns. Edgar Eldridge, founding member of the Barrington group composed a letter to the local circuit minister, the Rev Bill Norman, outlining their objection to the use of these "decadent" chords. There was an altercation outside the General Stores between Norman and Eldridge on 2nd November 1924 which resulted in Elridge composing a letter. On 3rd November 1924, the Broad Barringtons gather round the local Post Office daring Eldridge to send the letter i.e "push the envelope." This led to the famous pub song "Push The Envelope Edgar" which is still sung by ruddy-faced cider drinkers in the East Anglia area to this day. It also led to the expression in question.
