When the black chief-in-waiting of one of Botswana’s most powerful tribes married a white British clerk, they faced uproar and exile in an apartheid-era world. Jessamy Calkin meets the filmmakers and family members bringing their story to the big screen

There are three cinemas in Botswana, a country of 2.2 million people and three million cows. At one of them, in the Riverwalk Mall in the capital, Gaborone, an auspicious event is taking place: the African premiere of Amma Asante’s film A United Kingdom, starring David Oyelowo as Seretse Khama, Botswana’s first president, and Rosamund Pike as his white British wife, Ruth.

The event is part of a 50th-anniversary celebration of Botswana’s independence, a four-day affair that takes place all over the country and includes spectacular displays representing every aspect of its cultural life. Botswana is a lovely country. It could reasonably be said that it is one of the most stable African states.

Historically, it was less heavily colonised than much of the continent, and this has had a positive influence on it culturally. Good management and wealth brought by the discovery of diamonds have ensured that its citizens are entitled to free healthcare and education, and each can claim a piece of land, 40m by 40m, once they are 21, for which they don’t have to pay. (In two days here, I have met many people who have done so.)