The film industry is "doubly testing" of women and constantly questions their capabilities, according to Oscar nominee Rosamund Pike.
Rosamund, 37, said she was proud to be starring in the first film directed by a black woman to open the BFI London Film Festival, as A United Kingdom received a gala premiere in the capital.
Rosamund, who is a mother of two and received an Academy Award nod for her starring role in Gone Girl, plays the British office worker who fell in love with and married Seretse Khama, King of Bechuanaland, now modern Botswana, in 1948 in the face of fierce opposition from their families and government.
The film was made by Belle director Amma Asante and, arriving at the premiere, Rosamund said: "This is the first time the festival has had a black female director open the festival, that is huge. She deserves every success she gets.
"It's not easy being a woman in this business, it really isn't. Even if there is a gap between the films you make, people ask why or question you.
"I think they are doubly testing of a woman. It's also hard from an actor's point of view to be a person of colour, there aren't as many roles.
"It's fine to be the second lead but it's not always so easy to be the lead."
Amma said the premiere felt like a "monumental" moment, adding: "I've been trying not to think about it because it becomes so overwhelming.
"It's a full circle moment because 12 years ago I had my first film here, and never did I imagine I would be back with the opening film."
She continued: "I'm hoping this is not a one-moment wonder but is changing the tide and there will be many more (black female directors) after me. We have to keep our foot on that pedal."
Amma said she never could have imagined that the racial conflicts shown in the film would be so relevant to a modern audience, adding: "When this film was being put together long ago nobody could have dreamt we would be on our way towards a Brexit, or some of the occurrences in the news were going to be happening.
"Film has a responsibility to reflect the society that we live in and sometimes that happens by itself, we don't even conspire to be that way."
Selma star David Oyelowo, who plays the African king and serves as a producer, said the recent rise in racist rhetoric has made the film even more important.
He said: "It validates the reason for making the film, it's a shame that we are still in times when race is at the forefront of people's minds and not in the best of ways.
"But we are also highlighting the story of two people who saw beyond race and their love that helped them overcome all those obstacles and that is what we need now and that is what will make the change."
A United Kingdom is released in UK cinemas on November 25.