On The Basis Of Sex star Felicity Jones has said she wants “transparency” when it comes to equal pay in Hollywood.

The British actress plays Supreme Court Justice Ruth Bader Ginsburg in the legal biopic, while Armie Hammer stars as her husband, Martin.

Considered by many in the US to be a feminist icon, Justice Ginsburg was the second woman to be nominated to the highest court in the country and has spent her much of her career calling for gender equality.

Felicity Jones - On The Basis Of SexFelicity Jones stars as Justice Ruth Bader Ginsburg in legal biopic On The Basis Of Sex (Ian West/PA)

On The Basis Of Sex features her fight to overturn a law that discriminates against women.

Amid a debate over gender pay parity in the entertainment industry, Jones – who describes Justice Ginsburg as “a heroine of mine” – said it is “frustrating” when the issue is “brushed under the carpet”.

She told the Press Association: “It’s just transparency, that’s what you’re looking for. Obviously depending on the size of the role and that sort of thing, we’re not all going to be paid the same.

“But you want to make sure that when the role is of equal size of a male counterpart, there is an equality and that there is at least a transparency.

“Where you go, ‘OK I know what the situation is here’. I think that’s what’s frustrating, when it feels like everything is brushed under the carpet.”

Armie Hammer Armie Hammer stars alongside Felicity Jones in On The Basis Of Sex (Isabel Infantes/PA)

Jones, also known for starring in films including The Theory Of Everything and Rogue One: A Star Wars Story, plays a young Justice Ginsburg in On The Basis Of Sex.

The film tells the story of Justice Ginsburg’s early career, beginning with her struggles while one of the few women studying at Harvard Law School.

Now a household name in the US, Justice Ginsburg, 85, has become a cult figure among many young people, earning the nickname The Notorious RBG, inspired by the rapper Notorious BIG.

Jones, 35, said being British gave her an advantage in playing the role because she felt like an “outsider” on set.

She said: “On set I was the only Brit and I was an outsider, I could channel that into understanding what it was like for being Ruth because she was always an outsider, she was always in the minority.

Supreme Court GinsburgJustice Ruth Bader Ginsburg, whose early life and career has been made into a film starring Felicity Jones (AP Photo/J Scott Applewhite)

“So I actually think it really helped me have the right perspective and I think it was an advantage in some ways.”

Birmingham-born Jones’s co-star Hammer stars as Justice Ginsburg’s husband Martin, who was also a lawyer and who encourages his wife to pursue a career in law.

The US actor, who previously starred in The Social Network and Call Me By Your Name, said he is excited for his young daughter to see the film.

He said: “This is one of the first movies I’ve made my daughter can actually see. That’s one of the reasons why I took this, I loved the idea of a story of a woman who changed the world without superpowers, this is a woman who just used her brain and she navigated the world she was in, which was a man’s world, as we still are dealing with now.

“But my daughter will grow up to live in the world we are creating for her right now which is kind of scary. With Ruth Bader Ginsburg as an example, I think it’s good for her to see.”

On The Basis Of Sex, which also stars Justin Theroux, Jack Reynor and Kathy Bates, is out in the UK now.