I'm happy to accept a correction that that approach was more to do with the Singers Club, but I've heard direct testimony from a few who took part about this requirement, and how onerous it was.

According to Peggy (who I definitely believe), it was indeed a Singers' Club policy. However, many other clubs followed and became 'Policy Clubs'. It might have seemed onerous to some, but it was the Policy that persuaded people like Sandra Kerr and Lou Killen to look for songs from their own localities, and fuelled an interest in English folk song more generally. But for that, perhaps we'd all be singing Leadbelly songs to this day...