Between series 4 "Let there be light" episode, and this episode of series 5, there were two more special episodes. During the two years' gap, two one-off extended self-contained Christmas Specials, referred to as "Sea Fever" and "Angel Gabriel Blue", could unofficially also be considered to be episodes 8 and 9 of series 4, as they happen before the start of series 5. Additionally, and somewhat confusingly, in part as they are also the middle Christmas Specials 2 and 3 of the 4 Specials, they are usually skipped over from standard showings due to the extended length.
Episode was filmed in Great Yarmouth