The scene in which Young Carl sulks about Marianne was originally supposed to be about eight seconds long and contain nothing but Tom Sturridge sitting on a bench and looking sad. Will Adamsdale and Ike Hamilton happened to be there, so executive producer, writer, and director Richard Curtis told them to have a go at what they would have done if their friend was in the same situation. He put on "So Long, Marianne" and they came up with everything that remains in the scene.
This movie was loosely based on Radio Caroline, a popular pirate radio ship with a similar history and style. It was executive producer, writer, and director Richard Curtis' intention to weave a fictional story around the many pirate stations of that era, rather than base the story on fact.
The real pirate radio station Radio Caroline lent a great deal of the equipment seen on the ship. Although the turntables and broadcasting equipment is predominantly from the late sixties to the early seventies, it wasn't used on Radio Caroline until the 1980s.
The scene with Midnight Mark and all of his naked groupies (cut from the U.S. release) is an homage to the U.K. album cover of Jimi Hendrix's album "Electric Ladyland", even down to the placement of the girls.
Scenes were filmed with James Corden as a rival DJ from the new pirate station Radio Sunshine, sabotaged by the Radio Rock crew. These were cut from the movie, but are available as deleted scenes included on most home video releases.