In the Cotswolds, the Morris Tradition is very much at the end of May. It used to be that all the teams danced on Whit Monday, but that has now transmogrified to the "Late May Bank Holiday", i.e the last Monday in May when most of the Cotswold sides turn out. That's according to tradition but these days of course, they turn out all the summer, roughly coinciding with the cricket season. A lot of teams now turn out on 1st May, but that's a new tradition. Nothing to do with Beltane, which I believe is something Celtic.

Gwilym