The book has got millions of readers across the world hot under the collar with its depiction of the kinky relationship between a handsome billionaire and his willing sex slave. But the suspicion that the forthcoming film adaptation of Fifty Shades of Grey will water down the BDSM tilt of EL James’s novel appears to have been confirmed after the upcoming film escaped the most restrictive NC-17 rating from US censors.

Sam Taylor-Johnson’s film, which features “strong sexual content including dialogue, some unusual behavior and graphic nudity”, according to US film censor the MPAA, has been handed an “R” rating. That means those under 17 will need a chaperone in the form of a parent or guardian to see it.

An NC-17 rating often precludes cinema exhibition in more conservative parts of America. The R handed down by the MPAA suggests it features only “some adult material”, with parents “urged to learn more about the film before taking their young children with them”, according to the body’s own ratings guide.

Fifty Shades of Grey, which stars Jamie Dornan and Dakota Johnson as lovers Christian Grey and Anastasia Steele, is being released in time for Valentine’s Day on both sides of the Atlantic. Dornan has spoken of visiting real sex dungeons as research for the role, but rumours have abounded that the film features little in the way of genuine erotic tension. US critics reviewing early footage at the annual CinemaCon event in Las Vegas last March suggested most scenes centred on Grey and Steele, “making moon-eyes at each other”, with the film deemed “more romantic than sexual”.

Dornan confirmed in an interview with the Guardian in November that the film version would “appeal to as wide an audience as possible without grossing them out”, adding: “You don’t want to make something gratuitous, and ugly, and graphic.

“There were contracts in place that said that viewers wouldn’t be seeing my ... todger,” he said.