|Season 1, Episode 1|
|Air date||19 September 2003|
|Written by||Jesse Armstrong, Sam Bain|
|Directed by||Jeremy Wooding|
Warring Factions is the first ever episode of Peep Show. The episiode was broadcast for the first time on 19 September 2003.
Jeremy finally finishes his new song, This is Outrageous, and is very proud of himself. He is currently crushing on his next door neighbor Toni, which includes watching her from afar. Mark gets on the bus in hopes of seeing his work crush, Sophie, and she accidentally sits on his hand on the bus. Mark is too embarrassed and uncomfortable to remove his hand, which makes Sophie uneasy.
On his way home, Mark encounters some kids who call him "clean shirt" and try to provoke him into speaking to them, which results in them calling him a "paedo".
When Jeremy is out of the house with his bandmate, Super Hans, Mark makes his move on Toni and invites her back to his apartment to listen to Jeremy's music with the promise of Toni's favorite cereal, Alpen. Toni tells Mark that her sister has cancer, and Mark tries miserably to comfort her. They both end up laughing at Jeremy's song when they listen to it. When Jeremy walks in, he is furious at Mark and Toni, and expresses himself by writing "Judas" with raw meat on Mark's bed.
They later attend a party at Toni's house, where all of the attendees are random tenants from the apartment. Toni suggests playing party games but Mark and Jeremy are both more interested in finding ways to have sex with her. When Jeremy meets Toni's sister, Paula, he realizes she is in the music business and figures that if he sleeps with her, it could get him somewhere in his career. When Mark realizes that Paula is Toni's sister, he warns Jeremy that she has cancer. Jeremy suddenly feels reluctant to sleep with her, but obnoxiously offers her sex in exchange for career advancement, and makes a remark about her having cancer. It turns out that Paula is Toni's half-sister, and Toni's sister with cancer isn't at the party. Jeremy is angry at Mark because he believes Mark only said this to play a joke on him.
Mark and Jeremy are ejected from the party after humiliating themselves and Paula, and they go home defeated. The next day, Mark finally confronts the obnoxious kids by chasing them down the street, which Sophie sees through the window of the bus.