The vast majority of them are written by one guy, the shows creator, Charlie Brooker[1]. He's a UK comedian who has written a number of great shows such as "Screenwipe"[3] (a comedy documentary about the TV industry), "A Touch of Cloth"[4] (crime drama satire) and "Nathan Barley"[5] (which pokes fun at the London hipster scene and was co-written by Chris Morris[2] who is another UK TV legend)

[1] https://en.wikipedia.org/wiki/Charlie_Brooker

[2] https://en.wikipedia.org/wiki/Chris_Morris_(satirist)

[3] http://www.imdb.com/title/tt0780206/ (Screenwipe)

[4] http://www.imdb.com/title/tt2240991/ (A Touch Of Cloth)

[5] http://www.imdb.com/title/tt0426654/ (Nathan Barley)