I go off plan, I'm on plan or close to it the rest of the year. I enjoy my Christmas without worrying about syns, I know you can enjoy yourself without going off plan but personally to me Christmas is the one time I don't think you should diet.
I gained 7lbs last Christmas, hoping not to gain that much but if I do I do, its not the end of the world, its a bit of weight that only I notice, noone else could tell any difference and I know I can jump straight back on slimming world and loose it again.