I think Art Brooks has well articulated that the setting of UK folk clubs is very different from our informal song circles in living rooms. Very different contexts. It does sound like these are venues that serve to provide many folks with an opportunity to perform.

I think there is also a difference between a song circle where it becomes the norm for everyone to sing out of a standard songbook, be it RUS or any other book, and a song circle, such as Art describes, where some folks need lyrics or prompts for at least some songs, and some use nothing.

I do not particularly enjoy "group sings" where there is the expectation that everyone will sing along with every song, and the use of a standard book, RUS or otherwise, might be common.   For one thing, my voice is very low pitched. Whether it is congregational singing in church or a group sing, chances are it is going to be pitched in a key I can not join in on comfortably, or if it is my turn to lead a song, few people are going to be able to comfortably sing along in a key that works for me. doesn't mean I am opposed to them occurring. Just means I won't be there.