As far as playing tunes in sessions goes the same tune can be played at a variety of speeds giving it different feels. And the polite session player should take their timing from the person who starts the tune.
But Mr. Happy has made some incorrect statements about Have-a-Go in Chester.
Although I called it a "music and dance session" it is not a free-for-all that runs itself. I co-ordinate those who want to call, and try to persuade them to tell me in advance what tune they want so that our DEFINITELY NOT "self appointed" band leader can arrange the music and put it on her website for download, also make midi files so that those who want to hear the tunes in advance can play them.
She negotiates tempo with the callers and leads the musicians. First at practise speed, then at dance speed. Even so it is difficult to keep everyone together, the loud melodeon is vital.
Different dances need different speeds, and the comments from those who have actually danced or called have more often been "that was too slow". Yes, the callers are learning, it is a difficult skill to know what speed a dance needs, it is also an art to phrase the call so that the dancers know which part of the music fits which part of the dance - this can lead to dancers getting behind the phrase.
We don't only dance Playford, we dance a mix. Some dances are walked (with a smooth fast step) which needs much faster music the a stepped polka or bouncy hornpipe. As Dave MacKenkie said "if you play too slow the dancers will fall over!". I've been to a dance like that, some orchestral players got together to form a barn dance band, at their first gig it felt as if we had to stay in the air far too long.
At our age we can't dance hornpipes all evening and some of us still want to dance, not sit on the sidelines.