Cillian Murphy insists his sex scenes with Florence Pugh in ‘Oppenheimer’ are not “gratuitous”.

The 47-year-old actor obsessively lost weight to play the part of the father of the atomic bomb, J Robert Oppenheimer, in Christopher Nolan’s epic biopic on hre scientist’s life, and is seen bedding Florence’s real-life psychiatrist character in the film.

Cillian told the Sydney Morning Herald about how his on-screen romps with the 27-year-old actress are so “f****** powerful”: “Those scenes were written deliberately. (Christopher) knew that those scenes would get the movie the rating that it got.

“And I think when you see it, it’s so f****** powerful. And they’re not gratuitous. They’re perfect. And Florence is just amazing.”

Florence plays Communist Party member Jean Tatlock in the film, which also shows Oppenheimer’s marriage to wife Katherine ‘Kitty’ Oppenheimer, played by Emily Blunt, 40.

The sex scenes have earned the movie a 15 rating in cinemas due to what censors have called “infrequent nudity and sexual content”.

‘Peaky Blinders’ star Cillian – who has two sons with his wife Yvonne McGuinness, 50, who he married in 2004 – added about ‘Midsommar’ actress Florence: “I have loved Florence’s work since Lady Macbeth and I think she’s f****** phenomenal.

“She has this presence as a person and on screen that is staggering. The impact she has (in ‘Oppenheimer’) for the size of the role, it’s quite devastating.”

Director Christopher, 52, has admitted he was “appropriately nervous” and “appropriately careful” while making ‘Oppenheimer’, which saw his first effort at shooting sex scenes.

He told Insider: “Any time you’re challenging yourself to work in areas you haven’t worked in before, you should be appropriately nervous and appropriately careful and planned and prepared.

“When you look at Oppenheimer’s life and you look at his story, that aspect of his life, the aspect of his sexuality, his way with women, the charm that he exuded, it’s an essential part of his story.”