My father, Bill Stallybrass, first heard about this idea, this movement, in 1936. He was travelling by train from London to Paris, to bicycle down the Rhone valley from its source in Switzerland to the Mediterranean, and he shared a compartment with Philippe Mottu and two other young Swiss travelling home after an Oxford Group meeting in Birmingham. The friendship lasted until the end of their lives.
He also helped with the travel arrangements for that first summer in Caux during his de-mobilization leave from the British army, and I found his name among the participants in that first summer in 1946.