The inspiration for Amma Asante’s latest movie Belle sprang from an 18th century portrait that once hung in Kenwood House.

If it wasn’t for the painting of Dido Elizabeth Belle and her cousin Lady Elizabeth Murray, no-one would know the extraordinary story of how Lord Mansfield’s mixed race illegitimate great-niece was raised as an aristocrat at the Hampstead mansion.

Although most contemporary paintings depict people of colour as subservient, the two women are clearly shown as friends and equals.

Belle – (20th Century Fox, in cinemas tomorrow) – is loosely based on how Dido, the daughter of an enslaved woman and Lord Mansfield’s nephew, came to live at Kenwood and to influence his ruling in an important case that helped to end slavery in Britain.

Asante’s movie – which due to the house’s restoration last year wasn’t filmed at Kenwood – explores the tension between Belle’s aristocratic lineage which gives her certain privileges, and the colour of her skin which prevents her from fully taking part in society – as she struggles with questions of love, class, identity and acceptance in a country whose economy centred upon the slave trade.

“Everything you see in the film, the vision I have created, comes from the painting,” says Asante.

“Had I not had it, I don’t know how I would have gone about telling this story.

Emotions evoked

“The emotion it evoked from me, the questions I had seeing it, knowing how unusual and rare it was – who was she, why is she there and most importantly, who was the brave person who commissioned it? – were what drove me to make the film.

“For me, there was a lot of love in the painting, in the relationship between these two girls. The two words that sprang to mind, and what I hope people will take from the film, were courage and love.”

The 1779 unsigned painting inspired a 2007 exhibition at Kenwood to mark the bicentennial of the abolition of the slave trade, and Lord Mansfield’s – then Lord Chief Justice – part in inspiring the abolitionist movement via key legal rulings.

The centrepiece was the loan of the artwork which hangs at Scone Palace in Scotland.

In Belle, the landmark case of the slave ship Zong, when slaves were thrown overboard to drown, then claimed for on insurance, forms the climax to the movie as fiery young legal apprentice John Davinier (Sam Reid) uses it to draw attention to slavery’s inhumanity.

Gugu Mbatha-Raw’s Dido, caught up in the marriage games and status-seeking of the era, falls for Davinier as she begins to understand her own conflicted identity.

Asante wanted to bring provocative questions of race and justice to the usual marital manoeuvring of the romantic period film.

“I’ve never seen a film about the Jane Austen elements – the marriage market, the lives of girls growing up into society ladies, the romantic longing – combined with a story about slavery.

“Dido transforms from a girl who says, ‘As you wish, sir’, to a woman who says, ‘As I wish’, not because she is a privileged young woman who wants more, but because she is a woman saying, ‘I want equality in my household and in the world.’”

“I like to make films focusing on the grey areas of life and Dido has such a complex identity – she is this contradiction of black and white, the child of a slave yet an aristocrat raised in high society, of outsider and insider.

“Through her journey with John, she comes to learn who she is, where she fits in, what she wants out of life. The love story may be what draws people in but I hope audiences will leave the cinema with a whole lot more.”

Asante says illegitimate mixed-race children were often brought into households as servants, and Lord and Lady Mansfield showed great courage in not following that path.

“He didn’t choose to make Dido a servant, or to hide her – he chose to make her a central part of the family, to enshrine her in the painting. I’m in awe of the courage that must have taken, but there was complexity in that. Dido couldn’t eat with the family when guests were present because even if they chose to disregard society’s rules they couldn’t inflict that decision on other people.

“We will never know whether Dido had an influence on Lord Mansfield’s decision in the Zong case but we do know that he presided over other cases that had an impact on the stability of slavery and in the Somersett case, he made a moral judgement against slavery. He was an extraordinary man, a pillar of the establishment, a man of rules and yet progressive and ahead of his time.”

Struggles of many

She hopes that audiences perceive the end of slavery rested on no single person. The legal battles were vital, but so too were the struggles of many whose stories are lost to history, as Dido’s almost was.

“I hope people will take from this story that slavery didn’t end just by the white majority saying no. I like Belle because she also said no, and I think it’s very important that black people in history are given their own voices.”

Asante says ultimately Dido learns to live with her contradictions, just as she herself has done.

“Identities aren’t simple but that’s what makes us interesting and we need to look on those elements as a positive.

“Being bi-cultural growing up in 70s and 80s England with Ghanaian heritage, I always felt an outsider, not quite English nor African. But as I’ve got older, I now stake my claim on being British. I am black and British, that’s how it is and I like it.”

She believes it’s important to recover stories like Dido’s, which show that dual-heritage isn’t a contemporary concept and that “people of different races even then did fall in love and there were children born of loving unions”.

“I am not the shape, colour or package of most film directors. It’s a slow, challenging process, we haven’t rounded any kind of corner, but we have made some movement in changing the profile and background of the people telling stories.

“When you allow the diversity of Britain – not just colour but gender – to come through in the talent behind the camera it will follow through to the kind of stories we see on stage and screen.

“We have had stories being told for so long by people who look a certain way and if we keep looking at everything through the same lens we are only going to get the same stories.

“If we change the diversity of that lens, I hope we will see more interesting stories.”