Jim, performers in the club had to sing in their own accents and songs from their own background, or did that only apply to the residents ,nevertheless that is a rule.here in her own words in an article by colin irwin she explains this RULE
DOubtless contributing to that stereotype is the ban imposed by Peggy and Ewan at the club they were running in London in the early days of the folk revival on anyone performing material not of their own musical culture or heritage. Originally triggered by a heavily Americanised set at the club by Long John Baldry, it continues to inspire animated debate to this day. Peggy, who readily concedes that MacColl himself was singing American songs when she first met him, is unrepentant about their stance and sees no dichotomy in her current mash-ups with Broadcaster.

“I sing Scottish songs in the bath tub because they are so beautiful but I wouldn’t sing them on stage because I don’t feel qualified. I can’t pronounce them properly. I’d have to live up there for a long time. I’ve heard enough English and Scottish people singing Woody Guthrie and Leadbelly – and I was brought up with those songs – to know that I mustn’t sing Scottish songs in public. It would be too painful for the Scots to listen to.