from Wikipedia
For legal reasons, the production team were forced to make obviously fake banknotes for a scene. The £10 notes feature the Doctor's face and the phrase "I promise to pay the bearer on demand the sum of ten satsumas; no second chances, I'm that sort of a man". The text is a reference to the Doctor's actions and dialogue near the end of The Christmas Invasion. There were also £20 notes featuring producer Phil Collinson. These had the phrase "There's no point being grown up if you can't be childish sometimes." printed on them, originally spoken by the Fourth Doctor, Tom Baker. All notes, and the cash machine, were labelled "London Credit Bank".
Night filming of scenes involving gunfire, explosions and a tank disturbed some Cardiff residents, including one American woman returning home from the conflict in Israel.
Russell T. Davies had the idea for this episode from the very beginning of his association with the programme, and he planned to air it in Series Two. With the public announcement of two Christmas specials and the private knowledge of Billie Piper leaving at the end of Series Two, Davies decided to "elevate" this story to the Christmas special, not introducing the new companion immediately, and filling the slot with Tooth and Claw.
Guest star Sarah Parish's role is described as an "evil, alien mastermind".
Russell T. Davies, in his interview with Newsround, said that "Parish will be hard to recognise". This implies that her character will include prosthetics, covering her face. This is backed up by The Guardian Weekend Magazine in which Sarah Parish revealed that she plays "the Empress of Rachnos". According to Parish, the character is "half-woman, half-spider. It took four hours to apply all the prosthetics in the morning and an hour and a half to remove them at the end of the day".
Parish has co-starred alongside David Tennant in two other BBC One dramas — 2004's Blackpool and 2006's Recovery.
The "robot Santas" from The Christmas Invasion will return in this story.
According to issue 372 of Doctor Who Magazine, this episode contains the words Morocco, Biodamper, Lotto and "you can do the explaining, Martian boy".
