Poor Ewan/Jimmy was the butt of many jokes on the folkscene in the mid-60s (probably due to jealousy), when he was often referred to as "God". I think this came from a joke which went as follows:

A man knocks on the pearly gates and asks to come in to Heaven. St Peter asks him what he did on earth and he says that he was a doctor. "What sort of doctor ?", asks Peter. "A General Practioner", answers the man. "Oh we don't need any of those" says Peter, "Nobody ever gets ill here - go down to purgatory and come back in a thousand years". Another doctor, a gynecologist, asks for admission and is also sent down to purgatory because "No one gets pregnant up here". A third doctor asks for entry and when he tells Peter that he's a psychiatrist, Peter exclaims, "Come in we need you - God thinks he's Ewan McColl !".

I have also heard Ewan and Peggy called "Jimmy Miller and Mrs Campbell". While I won't go into the origins of this, a clue may be found in Cyril Tawney's song "New names for Old".