A United Kingdom: The interracial marriage that made front page news

A United Kingdom stars David Oyelowo and Rosamund Pike

Before she began working on her new film A United Kingdom, Amma Asante had never heard of Seretse Khama.

Now she's bringing his story to the big screen and hopes it will illuminate a seemingly forgotten part of British post-war history.

In 1947, Seretse Khama, an African prince training to be a lawyer in London, met and fell in love with Ruth Williams, an English bank clerk.

But their interracial relationship and plans to wed and return to Seretse's native Bechuanaland (modern Botswana) was greeted by fierce family and political opposition.

"We absolutely admit that none of us knew about this story before it came to us in the form of this project," says the film's director Amma Asante.

"Ten years ago financiers were saying we don't make period projects about unknown people - they wanted Mozarts and Churchills and people that you knew about.

"But that's been changing over the last few years and film is being allowed to expose stories that people haven't heard of and audiences are proving that that interests them."

Amma Asante with David Oyelowo

The project was brought to Asante by David Oyelowo, who plays Seretse in A United Kingdom opposite Rosamund Pike as Ruth.

Introducing the film to the audience at the Toronto International Film Festival, where it had its world premiere, Asante described Seretse and Ruth as "people who held onto life with both hands".

The film, she added, showed "the fall out that happened when they fell in love".

Asante expands on the subject when we meet in a Toronto bar the following day.

"Someone described Seretse and Ruth as the Burton and Taylor of their time," she laughs.

"She was this fashionable creature in these little black suits and he had this trilby hat. They were front page news."

Based on Susan Williams' book Colour Bar, A United Kingdom portrays how opposition to Seretse and Ruth's marriage went much wider than their immediate families.

The South African government - about to introduce apartheid - could not tolerate the idea of an interracial couple ruling a neighbouring country.

It pressured Britain to stop the union by threatening to cut off the supplies of the uranium and gold Britain needed for its nuclear programme and to rebuild its post-war economy.

'Highly politicised'

Asante, who grew up in south London as the child of Ghanaian immigrants, welcomes the number of other films on this year's festival circuit - such as The Birth of a Nation and Loving - that examine racial prejudice from a historical perspective.

"We are in highly politicised times," she says.

"America is just coming out of a period where it had its first black president and it might be about to vote in its first woman president.

"Britain just voted itself out of Europe. Some people said it had nothing to do with xenophobia, some people say it did.

"In these highly politicised times you get polarisation. There is very little in the middle. At that time the job of the film-maker is to reflect society and the conversations that are going on.

"A really tangible way to explore politics is through race."

David Oyelowo greets fans on the red carpet at the world premiere in Toronto, which was also attended by Seretse's grandson

It was important to Asante that the African scenes were filmed in Botswana. She used some of the actual locations associated with Seretse and Ruth, such as the house where they first lived.

"We had to put the house back together, literally. It was a derelict shell," she recalls.

"We recreated the looks of the rooms through old photographs. The hospital in the scene where Ruth gives birth to their baby is the actual hospital where Seretse was born."

How well is the story known in Botswana?

"Not as well as I thought," says Asante. "But I'm going to get lashed on Twitter from people saying 'you didn't get this right, you didn't get that right'.

"But, in the way that [Asante's previous film] Belle is now taught in schools, I hope this will also make a difference too, across Africa."

Seretse died in 1980, having been Botswana's first president since 1966. Ruth, who had been the First Lady of Botswana until her husband's death, died in 2002.

As our interview comes to an end, Asante reveals that Seretse's grandson had attended the premiere the previous night.

Furthermore, Seretse's son, Ian Khama, is now the fourth elected president of Botswana.

"We were in conversation with the president while we were making the film as well as many family members," says Asante. "They certainly didn't tell us the kind of film to make."

She recalls how President Khama arrived in his helicopter while they were filming in a village.

"I remember him looking out of the corner of his eye at Rosamund and David and saying, 'It's really weird to see your parents coming back to life'."

A United Kingdom opens in the UK on 25 November and will open the London Film Festival on 5 October.

The Toronto International Film Festival runs until 18 September.