Best singaround I ever went to was in Morpeth, many years ago. Went for the Gathering. It wasn't part of the formal event. Just a bunch of Morris men and singers having a fun singaround in a pub, completely unofficial. Fringe. I don't think we had an MC. We just went round the room, and when one singer had finished the next one round counted a beat or so and just started singing the next song. Went on for several hours. Mind you, I was sung out by the end...

There's a definitely a maximum number. At my local a week or two ago we got to 19 people and that was a squash. We had a new MC on and it was definitely a harsh debut. I didn't even get to perform - just too many people.