Hagman above said
Hull, Folk Union One The Folksons, who soon became the Watersons, opened their own club in 1959 in a dance hall. They moved on to Ye Old Blue Bell where in 1965 they and the folk club were featured in the BBC television documentary Travelling for a Living.
The BFI allows you to watch the whole 45 minutes of Travelling for a Living here
https://player.bfi.org.uk/free/film/watch-travelling-for-a-living-1966-online
I think the commentary refers to 2 or 3 hundred folk clubs but that seems a bit low.