Try looking up 'Lord of Misrule' (can't do it here, work computer doesn't like Google) - that will give a lot of traditions from Christmasses past, including that of mumming plays and morris dances done during the festivities.

If a group of men is needed to go around the outlying villages to 'mumm' or act out a play, what better than to use a morris group already established and with their own costumes or disguises? These mummers would 'guise up' (that is, disguise themselves) and go and perform for people for food, drink or the odd coin. If none were forthcoming then the group would play some little prank on leaving. That's how 'trick or treat' really started. We perform for you, you give us a treat or we play a trick on you. I daresay that if the group were the morris dancers then the entertainment might concievably be a dance or two as well as a mumming play.

These guisers were active in the darker months of the year, when pranks could be played with impunity, from Hallowe'en through to Candlemass usually, with the biggest opportunity for merrymaking being the 12 Days of Christmas.

I'm not at home, but when I get there, I'll look in my library and see what other possibilities and references I can find.

In the meantime, I can thoroughly recommend a book by Frank Muir, 'Christmas Customs and Traditions', which is brilliant and has almost all you need to know about the season fast approaching.

LTS