This Film Is Not Yet Rated (18) <!-- none onestar twostar threestar fourstar fivestar -->

The documentary This Film is Not Yet Rated offers a glimpse into the strange, puritanical, mindset of the Motion Picture Association of America (MPAA), an organisation that for nearly 40 years has rated and classified that nation's movies. Overseen until recently by the seemingly somewhat sinister Jack Valenti, a former aide of Lyndon B Johnson, the MPAA operates as a guardian of public morality, its members working in anonymity and handing down judgments without explanation or accountability.

The director Kirby Dick is plainly exasperated by this state of affairs, and interviews film-makers who have run foul of the outfit's high-handed and seemingly arbitrary adjudication. Kimberly Peirce, the director of Boys Don't Cry, had an NC-17 cert (a commercial death sentence) slapped on her movie because Chloë Sevigny's orgasm scene went on "too long". This is just one instance among many of the board's absurdly squeamish attitude to sex.

Matt Stone recalls how he and Trey Parker deliberately over-egged the puppet-sex scene in Team America: World Police to bamboozle the raters, who would end up cutting extraneous stuff while waving through most of what the directors actually wanted. Who can explain why sex and nudity are constantly penalised, while screen violence gets off virtually scot-free?

Dick tries to penetrate the MPAA's anonymity by hiring a private investigator and, in a Michael Moore-style stunt, submits his own film for classification (it gets an NC-17, without comment). His point is eventually proved - the board is autocratic, ridiculous and possibly corrupt - but you may feel worn down by his head-shaking indignation, the unvarying complaints of film-makers and the irrelevant profiling of his lesbian detective. The self-righteous tone may not win this film as many friends as he would like.