The Detection Club was founded in 1928 by Anthony Berkeley. You can read a bit more about it and see who else are members on the gadetection wiki page. Simon Brett is the current President.
I wonder if this oath is still in use? It begins:
The Ruler shall say to the Candidate:
M.N., is it your firm desire to become a Member of the Detection Club?
Then the Candidate shall answer in a loud voice:
That is my desire.
Do you promise that your detectives shall well and truly detect the crimes presented to them, using those wits which it may please you to bestow upon them and not placing reliance on nor making use of Divine Revelation, Feminine Intuition, Mumbo-Jumbo, Jiggery-Pokery, Coincidence or the Act of God?
Do you solemnly swear never to conceal a vital clue from the reader?