The BFI London Film Festival made history on Wednesday by opening with Amma Asante’s biopic A United Kingdom, starring Rosamund Pike and David Oyelowo.

The film is the first directed by a black woman to open the annual festival and tells the real-life story of a British woman who fell in love with and married Seretse Khama, King of Bechuanaland.

Rosamund PikeRosamund Pike stars in A United Kingdom

Appearing at the festival Pike said she was proud to make history with the film and spoke of how hard it still is to be a woman in the industry.

"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,” Pike said.

"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,” the actress added.

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In the biopic PIke plays Ruth Williams, a British officer worker who falls in love with Seretse Khama, King of Bechuanaland, now modern Botswana.

Despite opposition from their families and government, the couple married in 1948, but had to spend years living as exiles in England, when Khama was prevented from returning home to Bechuanaland.

Asante, who also directed Belle, described the film opening the festival as a "monumental" moment. "I've been trying not to think about it because it becomes so overwhelming,” she added.

"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.”

Watch the trailer for A United Kingdom below: