Slavery? Any evidence?
He's a toff, remember. Father was a stockbroker. Major money was great, great grandfather who was a grain-trader on the Chicago exchange in the 1800s, but the family have been in politics and law since at least the 1600s, and he's the Queen's 5th cousin, once removed.
Don't you think if there was any attributable connection to family money coming from slave trade, it'd have been at least thrown at him by Labour, and probably by newspaper ftont pages too.