Perhaps the most decisive and influential blow against the slave trade was the evidence presented to various enquiries from men who knew the slave ships and plantations at first hand.
What these committee reports told of African suffering had a profound impact. They produced revulsion in those who read them and helped to win over armies of supporters to the abolitionists' side.
The enquiry set up by Pitt produced a 900-page report and detailed the evidence of abolitionist Thomas Clarkson.
In one particular example, Thomas Clarkson's argument that Africa had many goods worthy of trade was corroborated by fustian manufacturer John Hilton. Hilton had looked at a sample of cotton wool from Senegal, collected by Clarkson, and rated it highly.
Olaudah Equiano also expressed support for trade with Africa and wrote a letter to the Privy Council committee carrying out the enquiry.
Other evidence heard by subsequent committees was contradictory. Two witnesses gave evidence describing slave ships. Captain John Knox said that he had no knowledge of the kidnapping of slaves or obtaining slaves by fraud or oppression, whereas James Towne spoke of slaves shackled on overcrowded ships.