Continuity mistake: Roy closes his comic and throws it onto the desk. The camera flits back to Moss, then back to Roy, and Roy is holding the open comic again and repeats the same actions. (00:06:25)
Continuity mistake: Roy has scratches on his face from his and Moss' 'fight'. In the next scene, the scratches are gone. (00:15:30)
Continuity mistake: When Laura Knightly leans against Roy for the cameraman to take a couple photos, her face is even with Roy's. In the next shot she's above him so her chin is at Roy's eyes.
Continuity mistake: When Jerome pulls one of the disabled men out of his wheelchair, both of the disabled men on screen are in different wheelchairs to those they used in the scene where we first see them (when Roy files the police report).
Continuity mistake: Near the start when Moss runs and jumps onto the couch, his tie changes positions repeatedly between shots. In close-ups it is up on the couch arm and in all other shots it is under Moss.
Continuity mistake: Season 2, episode 5 "Smoke and Mirrors": Roy's lipstick alternates between bright pink and more of a peachier colour throughout the scenes.
Continuity mistake: Season 3 Episode 1 'From Hell' When Roy says "Nice glasses" and Moss replies with "Not as nice as your momma's glasses", The Red Door between Roy changes from being closed to being open.
Revealing mistake: When Moss runs into the door, all walls on the set shake. (00:06:25)
Friendface - S3-E5
Other mistake: In the beginning of the episode, Roy is explaining why Friendface is bad and chastising Jen for being on it. If you look at his monitor, he is on a website with a green color palette like the Friendface infomercial and a layout similar to MySpace. While I can't be 100% sure, it seems like a graphic designer created a mock website of Friendface to be used in the show. If true, that means Roy is already on Friendface before Jen even enters the room. (00:01:00)
Continuity mistake: The way Jen's books are stacked changes after she says "pedal stool." The book with the red pages moves to the top.
Answer: It's a joke on the "118" numbers in the UK. 118 numbers were used for directory enquiries and adverts for them on TV always tried to give a way to easily remember one for a particular company. The fake ad in the show takes it to the extreme. People in the UK do not use "911", the point of the joke was that Roy had forgotten "999" while saying it was easy to remember.