Seretse Khama and Ruth Williams did not have it easy. Their first problem was finding someone to marry them. When the ceremony was eventually performed at Kensington registry office in 1948, their families refused to attend. Worse was to come. Seretse Khama was also heir to the chiefdom of Bechuanaland, a British protectorate uncomfortably near the newly nationalist South Africa.

The couple became entangled in an unholy alliance between a weary post-war Britain and a rich, racist South Africa. Clement Atlee’s Labour government needed African gold and uranium and knew it wouldn’t get it if the black husband of a white woman was allowed to continue as chief in Bechuanaland, a title Seretse assumed in 1949.

So, the British Government took the shameful way out and banished the chief from his own country. It denied racism, but suppressed the results of its inquiry into the affair, which had declared Seretse fit to rule.

Exile for five years, they decreed. Then Winston Churchill’s Conservatives were elected and they made the banishment permanent. Fortunately, their crass politicking soon caught up with them. Across the world there was outcry at the treatment of the young couple and eventually, in 1956, the Government realised that Britain must distance itself from apartheid.

Seretse and Ruth were allowed home so long as he renounced his claim to leadership. For a while Seretse lived the quiet life of the common man.

Then, suddenly, in 1961 he was inspired to act again on the political stage. The Bechuanaland Democratic Party, with Seretse Khama at its head, won the country’s first full elections of 1965. The former exile became prime minister and then president of the new Republic of Botswana.

For the next 15 years, Botswana had the fastest growing economy in the world. It was a principled country, a defender of democracy and equality despite being surrounded by war and racism. Clearly its leader had decided to improve on the example that Britain had set him.