Rating: ***

Having made two successful real documentaries about the films of Terry Gilliam (The Hamster Factor and Lost In La Mancha), Keith Fulton and Louis Pepe have now made a fake one, or as they prefer to term it, a 'pseudomentary'.

Apparently the pair get a bit sulky about anyone mentioning either This Is Spinal Tap or Stuck On You in connection to their film, but given the storyline - conjoined twins form a band, then a woman comes between them and one of the brothers decides he wants to go solo - it's hard to see how you can avoid it.

However, while it may share several narrative and thematic elements and comes partially improvised, Brothers of the Head is a far different creature in terms of source, execution and tone.

It's certainly no comedy.

Based on a 1977 illustrated novel by the late Brian Aldiss, it uses "archive" documentary footage, contemporary interviews (with different actors playing the characters' older selves), and even spot on clips from a supposed uncompleted Ken Russell biopic (featuring Jonathan Pryce, John Simm and Jane Horrocks) to unfold the story of Tom and Barry Howe (played with raw intensity by identical twins Harry and Luke Treadaway).

Joined together at the stomach, the young Siamese twins who, discovered in their Norfolk fens home by an opportunistic exploitative impresario, enjoyed a brief burst of fame as punk duo The Bang Bang in the late 70s before the arrival of journalist Laura (Tania Emery) threw a romantic spanner into the already drugs and booze-riddled works, not to mention the brothers' sex lives.

Tom, it seems was the introspective quiet one while Barry was the wilder, angrier of the pair; their clashing personalities amusingly delineated by the former writing sensitive ballad My Friend and the other responding with punk thrash My Friend (You ****).

Veined with a thick seam of black humour that only infrequently stumbles into Tap silliness (notably with a thuggish manager who, literally, beats Barry into line), and with an atmospheric visual style that potently bears Gilliam's influence, it deftly catches the sordid nature of its milieu (far more successfully than the recent Stoned) while offering weighty psychological insights into the brothers' imposed co-dependency.

Working with songs written by noted producer (and New Wave veteran) Clive Langer, the Treadaways learned to play and sing from scratch just as do their characters, furthering the smell of authenticity their own fraternal relationship brings to their performances.

As with many a real rockumentary, it loses its grip somewhat in the home stretch as it heads for the predictable note of recalled tragedy; but offbeat, macabre, disturbing and at times emotionally churning, it makes for a hauntingly compelling experience.