‘Dr Livingstone, I presume?’ is one of those well-known phrases whose deeper significance is strangely elusive.

I first heard it as a child, while living in what was then called Tanganyika in the 1950s. Somewhere not so far away at Ujiji in that same country, one white man had once greeted another thus. The man who spoke the words was Henry Stanley, an American journalist with a questionable reputation. The other was the famous missionary and explorer Dr David Livingstone, who seemed to be one of the good guys.

But what were they doing there? Why the curiously stilted greeting? And why all the fuss? I realised it referred to an important moment in the exploration of Africa. But, so far as I was concerned, this was a place I romped through on a daily basis. It did not