Advertising posters showing a bloody hand sliding down a London Underground train window were banned from the Underground as being in bad taste, even though scenes had been filmed with permission in disused stations on the Underground. Producer Julie Baines found this "highly amusing" and "a bit ludicrous", noting that the film is "not based on real events - if it is, we are all in trouble." The ban was later removed, although not in time for the film's British opening.
Kelly Scott didn't see Sean Harris in full make-up as Craig until the sequence where Craig operates on Scott's character Mandy was filmed. As a result, many of Scott's reactions of fear and confusion were genuine.
In the scene with Jimmy and Kate on one of the trains, there's a dead guy (the train driver) lying on the floor. If you look closely you see he has a moustache. It was actually added on later using CGI so he wasn't confused with the previously killed security supervisor.