Bilbo Bagshot is the identical twin of Manny from Black BooksBlack Books and Spaced are proven to exist in the same universe, since in one episode of Black Books, Manny is heard talking to Twist Morgan. Because of this, the only reasonable explanation for why Bilbo and Manny (both played by the same actor, Bill Bailey) look so similar is that they are identical twins. Additionally, Tim is probably related to Evan, the manager of Goliath Books.
Darkstar Comix owns Two Thousand AD in the Spaced 'verse.Spaced is an alternate reality where Two Thousand AD's non-Megazine Spin Offs (Crisis, Revolver, etc.) succeeded and they were able to form a company of their own when they parted from Fleetway (as opposed to being bought by Rebellion, as in Real Life). A copy of Two Thousand AD is seen on Damien's desk and Tim's ambition is to work for Darkstar, even though he is established In-Universe to be a huge Two Thousand AD fanboy. Ergo, Damien Knox is Tharg.