How did a sugar boycott and a drawing of a ship help end Britain's slave trade?

It took a movement, and the movement used almost every tool a campaign can use. In 1787 a committee, mostly Quakers, formed to end the British slave trade. Its methods, according to the historical record, included first-hand accounts from formerly enslaved people, consumer boycotts of slave-produced goods, and petitions to Parliament.

The committee's most tireless researcher was Thomas Clarkson, who interviewed sailors and former slaves at ports such as Bristol, Liverpool and London. He then crossed the country setting up a network of 1,200 local abolition groups. A petition in 1792 collected 400,000 signatures. The Quakers who made up most of the committee could not sit in Parliament, so William Wilberforce, an Anglican, carried the cause inside it.

Ordinary households joined too. Women and children, groups that had never been political before, took part in the sugar boycott. Women could not vote, and often had to hold their own meetings because of rules against appearing in public ones, yet refusing to buy sugar was something they could do without a vote.

Then came images. An engraving of the slave ship Brookes, published in Plymouth in 1788, became an iconic picture of the trade's inhumanity. It is not an exact record: it shows 487 captives, while the ship carried 638, 744 and 609 on its neighbouring voyages.

Parliament still took years. The Commons voted for gradual abolition in 1792 and the Lords reversed it. The Slave Trade Act finally took effect on 1 May 1807, after 18 years of trying to pass an abolition bill. It ended the trade, but enslaved people could still be held within the Empire until the Slavery Abolition Act of 1833.