Having fortified himself with the first of several sips of brandy, Ignatius Sancho carefully settles himself into position. “One is sitting for one’s portrait,” he announces in the most upper crust of accents. The painter is Thomas Gainsborough, the year 1768, and Sancho is black. The first African known to have voted in a British election, he was forced to work as a child slave in Greenwich, rose to become butler to the prestigious Montagu family, then took a grocery shop in Westminster. Alongside this, he was a voluminous correspondent, composed music, and acted on the stage.

This real life character is tailor-made for a one-man show, and writer/actor Paterson Joseph, perhaps best known for his appearances in BBC TV’s Casualty, has taken on the task with evident relish. “Some of you have not had the privilege of entering into the world of the educated negro,” he says, bestowing a saucy and inviting grin. Wearing an exuberantly eye-catching wig, Joseph bears a considerable physical resemblance to Sancho as painted, a fact that he exploits to the full.

Joseph reveals in a programme note that he learnt less about Sancho from the letters than he did from the portrait: “His poise, humour, curiosity, and deep intelligence shine through.” Self-deprecating humour, in particular, shines through in Joseph’s performance, preventing Sancho from seeming too smug or self-satisfied. Persuaded to go on the stage by Garrick, his Othello was not a success. “I nearly hanged myself,” Sancho reveals.

So does Sancho harbour no bitterness about his early life, no feeling that he could have risen higher had he been white? Joseph suggests little of that verbally — his eyes, however, sometimes tell a more painful story. But the overriding message of Joseph’s engrossing play and performance is that life is what you make it, whatever the colour of your skin.