Dress code in a folk club? Hardly. Unless slightly scruffy is a dress code. I doubt if anyone could dress in a way that would make make for problems. Bare naked perhaps, but I'm not even sure about that - I once saw a team of Morris Dancers just dressed in strategically placed rubber balloons, though that was a a festival rather than a cluib..

Typically folk clubs will take place in a function room attached to a pub, though these are becoming increasingly hard to find. Pubs by definition are open to the public, that's what "public house" means. Sometimes they will lay down some kind of dress rules, like no muddy boots, or no caps with peaks, or keep your shirt on.

All kinds of drinks will be on sale in pubs, but mostly poeple drink beer, or soft drinks. Pubs have age limits, but that probably wouldn't apply to function rooms, I think.

And sometimes folk clubs operate away from pubs, for example one I know uses a church vestry, another a room in a British Legion (army veterans) club. In both cases there's a bar.