Hi again; this is really helpful! Dick; I agree about the nature of a lot of sessions; what prompted the thinking here was that this session has distinct elements of performance in it, with lots of interaction with the crowd, a fairly high level of musicianship and lots of variety in terms of material (I heard a Richard Thompson song, bluegrass, a couple of Irish reels, a trad unaccompanied ballad and Hendrix's version of Hey Joe in quick succession on Monday!). The core members of the session have played together every Monday for eight years, so there is an element of 'rehearsal' in there too. The landlord of the pub takes a leading role as a kind of MC as well as playing, so there is a sense of organisation as well. Players and singers know when to join in or sit out, without the nered for explicit 'stage directions'. I also agree about the need for some careful thought to make it look and sound 'natural'.
I'm still looking for suggestions about UK festivals who might be receptive to this idea!
Tim