What is the origin of the British holiday tradition of the 12th night?

Question

My grandmother says that it is a British tradition that includes taking decorations down 12 days after Christmas is over.

Answer 1

It's fairly international, not just British. Twelve days from 25th December is 6th January - the day that the three wise men visited Jesus. That is when the festive period ends, and the decorations come down. Here's wikipedia ....
http://en.wikipedia.org/wiki/Epiphany_%28Christian%29

Answer 2

While it is a British tradition, it is also celebrated in other countries. I think Britian might make the biggest deal out of it. It does coincide with the Feast of Epiphany as noted by another answerer. In France, the 12 days of Christmas end on 12th night when the last and final gift is given (they give one gift a night for 12 nights starting on Christmas). It started in medieval times when the end of the Christmas season was celebrated with a large banquet by the King before the nobles who had celebrated the season with him went back to their own estates.