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For the purveyors of the most famous erotic film franchise in history, the bosses behind bonkbuster Fifty Shades Darker are oddly prudish.

I can reveal that execs at Universal Pictures have banned the cast from making sexual and graphic references in their promo interviews.

The BDSM film’s stars including Jamie Dornan and Dakota Johnson have been forbidden from any kinky talk and forced to push the romantic elements of the movie instead.

Oscar-winner Marcia Gay Harden, who plays the mother of Jamie’s character Christian Grey, let slip the stuffy stipulations after landing herself in trouble for jokingly tweeting about sex toys.

In a new, thankfully unfiltered interview, Marcia said: “We can’t talk too much about nipple clamps.”

“I used to send out some naughty little tweets, along the lines of this ‘sweater clasp’ and I was told by Universal that I couldn’t do it any more, but I’ll tell you one anyway.”

“I’m a good girl, I fell in line. Because it’s supposed to be more about the ‘romance’.”

“Maybe I went too far … I don’t know.”

“I sent out a picture of a sex toy and I was like, ‘Dear Christian, thank you so much for that lovely bracelet under the Christmas tree. Perhaps it wasn’t meant for me.”

‘Oh well, so pretty.’

“And all the fans would write back, ‘No that wasn’t for you Mama Grey, oh no.’ That was a lot of fun but it was shut down.”

“It is a love story after all — I don’t think they want us being too overtly sexual in interviews.”

The Sun told last week how the sequel to Fifty Shades is far raunchier, with 15 minutes of erotic action including two bondage scenes.

One graphic, X-rated moment involving a sex toy lasts almost three minutes and had members of the audience at last week’s LA premiere laughing and screaming in horror.

Another explicit scene sees Dakota’s character Anastasia Steele strapped to a stainless steel bondage bar with foot restraints for a love-making session in Christian Grey’s infamous Red Room of Pain.

The film’s UK premiere is in London on Thursday before hitting screens here the following day.

It’s a clean, family-friendly, romantic flick . . . honest.