Brothers of the Head is a cod rockumentary by Keith Fulton and Louis Pepe, the pair responsible for the revealing authentic documentary Lost in La Mancha.
It traces the careers of conjoined twins from a desolate area of East Anglia (they're played by identical twins, Harry and Luke Treadaway) who enjoyed a brief career as punk rock musicians in the 1970s.
I didn't get the point or the joke.