"Guest, Observer-But they would be far better in terms of quality of performance, and you never know it might just encourage the ring-binder and i-pad brigade to actually make the effort to actually learn a song".

Or not bother turning up at all.
Alternatively, they could start up a rival "Ring-binders Only Club" ;-)

Personally, I don't think Folk Clubs should put up any unnecessary walls around their sessions. They are social gatherings, not military exercises.