doesn't help us to recognise a piece of music as being "folk" - which is the purpose of a definition.

If the definition of Flotsam is some anomalous artefact adrift in the sea, then the definition of Folk I'm suggesting is valid as a definition. It might define the music in terms of genre, but it does define the music in terms of its human & social context which I would have thought was more important to a music called Folk. The 1954 Definition does that too - it never once nails a genre as such, just gives a catalogue of criteria by which a song might be considered Folk. So Folk has always been a matter of contextual criteria rather than musical content - it has never been a genre as such, more of a construct.

Do the George Formby uke-players or classical guitarists really believe their music is folk, therefore they go to a folk club to play it? My guess is they think, "OK, this isn't folk, but if I go to that particular folk club they'll let me play it anyway."

My guess is they come because a folk club is one of few places they can get to play their music to an appreciative & warm hearted audience, which is generally what you find in a folk club and why the music - any music - tends to be accepted as such.

What you have done is to define the music policy for your club.

Not just our club - all clubs & festivals are like this to a greater or lesser extent. It's the wider condition of this thing called Folk Music.

By extrapolating from that to claiming that all music is folk music you are implying that all folk clubs should have the same policy

I've yet to go to one that doesn't. In fact - if there's anyone reading this who knows of an exclusively Traditional Folk Club or Singaround I'd be interested in hearing about it - if only so I might come along one day!

and that any "folk club" which turns away the uke-players or classical guitarists has no grounds for doing so.

I can't conceive of any such club. Seriously - in my time I've been to hundreds of clubs, and even the most traditional of them wouldn't be so callous as to turn anyone away. That is one of defining attributes of Folk Music - inclusiveness on a human level.