Matt Smith says -
I've always wanted to be part of the Christmas Doctor Who experience, and I think this is certainly one of the most Christmassy and inventive Doctor Who stories so far. Steven just keeps getting even more imaginative and the great thing about this episode is that when Doctor Who and Christmas are put together you combine the spirit of both those things; it's a fun old yarn and the Doctor simply loves Christmas.
It was a real privilege to work with Michael (Gambon). I had a great time with him and he was really naughty! He's so crafty and when I asked him about working with iconic actors such as Olivier and Bates he said the one thing they all had in common was they were naughty – and he's exactly the same. He was very mischievous, constantly telling jokes and getting into the spirit of play.With Katherine I was astounded by her professionalism. Considering it was her first acting experience I thought she handled it with real craft and diligence. It's exactly the type of casting we want; someone fresh, exciting and new