Jim,
you say "I know of no club organisers who encourage singers to perform material that is not in line with club policy."

Herga is such a club. Its reputation and the vast majority of its residents lean towards traditional, but we encourage everyone to sing whatever they like, and we enjoy some excellent jazz guitar and contemporary songs from Chris Flegg, the occasional contemporary duet from Moses and the Ref, other contemporary singer/songwriter stuff... And yet, when we want to put on our "best face", the club is unmistakably traditional, with the likes of Johnny Collins, George Clarke, Kitty Vernon, Mike Sparks, Graeme Knights, etc. I am a permanent aberration, in that respect, yet one the club encouraged and fostered and helped. Which is precisely the reason why "Friends like these" was written for those very folks I just mentioned: traddies, but welcoming everything.