David Lammy, the UK Foreign Secretary, is on a visit to Nigeria and South Africa this week. He’s there to strengthen the UK's trade relations with African countries and to talk about the past mistakes of British involvement in the transatlantic slave trade. Just a week ago, leaders from 56 Commonwealth countries signed a document calling for discussions about reparations for slavery, making this a very timely visit.

In Lagos, Nigeria, Lammy called the transatlantic slave trade "horrific ...