The tent has been decorated and the invitations have been sent out for two very special Christmas episodes of "The Great British Bake Off," featuring returning contestants from previous years. A festive welcome awaits four more returning bakers - Chetna from Series 5, Howard from Series 4, James M from Series 3 and Janet from Series 2.The judges have set three festive challenges, starting with a savoury signature to get the Christmas party started. In the technical, Paul has a gifted them a bread challenge that's not for the faint-hearted. The final challenge, the showstopper, is huge, as the judges lay the festive gauntlet and ask the bakers to make a trio of Christmas favourites. But who will hold their nerve and produce the perfect desserts?