The drama focuses on a 15-year-old girl, played by Bel Powley, who embarks on a scandalous relationship with her mother's 35-year-old boyfriend, played by True Blood hunk Skarsgard. Wiig plays the mother.

The controversial plot point has prompted censors at the British Board of Film Classification (BBFC) in the U.K. to give the movie a restrictive 18 certificate, much to the disappointment of director Marielle Heller, who insists it is aimed at teenage girls.

The ruling reads, "Diary Of A Teenage Girl has been classified 18 for 'strong sex'. The sex scenes and references are too numerous and sustained for a 15 classification to have been defensible."

Heller says in a statement, "A girl's coming of age is rarely seen on screen or given the same treatment as a boy's... Boys are given so many examples of films that say whatever they feel sexually is normal... As girls, we have been trained for a long time to relate to a male protagonist, to feel their stories and to be invested in them. And there's no reason why we can't invest in female characters the same way. Sexuality is something we're both experiencing and so if one side's perspective is reflected, the other side should be reflected too. Women's stories should be explored and celebrated too."

A statement from the distributor behind the movie, Vertigo Films, adds, "We are massively disappointed with the final ruling. The film has been viewed by men at the BBFC and we feel that they have missed the point of the film and its message...

"In an age where young women are still continually being sexualised and objectified we feel The Diary Of A Teenage Girl sends a very positive, reassuring message to young girls about female sexuality and body image. It is a shame that audiences will not be able legally to see a film that was made by women for women of all ages."

The Diary Of A Teenage Girl hits cinemas in U.K. and U.S., where it has been given a restrictive R rating, on 7 August (15).