It�s a bit of entertainment, a Christmas show, something for the children of faith schools and their parents to look forward to. It is not part of our cultural heritage as such and since as said above �most� of the UK does not recognise the sanctity of Christmas and the Nativity as Christians do anyway - it really has no place anywhere other than in faith schools or churches.
Personally I enjoy them, but then I enjoy a lot of the shows the schools of my nieces and nephews put on. It is a jolly good night out. As said by Jake, if you want it, complain, if you don�t, then don�t. If your child goes to a faith school and they are not doing a nativity, then ask them why. If they are not a faith school, then one would assume some other form of Christmas show is laid on? JStO maybe?!