I have a recording of the altercation Vic.
MacColl was chairman and was summing up what had been said when Davenport began talking loudly over him (he had done the same over a number of speakers from the floor - seems common practice with him, He did similar to an Irish language singer at the Musical Traditions club because she had the temerity to explain (briefly) her songs - "I came here to listen to singing not ******* talk; thought we'd got rid of this **** back in the sixties".
The explosion at the John Snow took place when one of the audience said he thought Jeannie Robertson was a wonderful singer - Bob described her as "terrible".
Can't say for certain that there was violence - sounds as if the protagonists were restrained by onlookers.
Jim Carroll