After Parliament rejected the abolition bill in 1791, abolitionists took action by sidestepping Parliament entirely and calling for a boycott on Britain's largest import, slave-grown sugar.
The Transatlantic Slave Trade flourished because a market existed for produce created using enslaved labour:- rum, cotton, tobacco, coffee and particularly sugar. The abolitionists understood that profits from the sugar they used in tea or cakes kept the Slave Trade running.
If economic pressure could be put on slave-dependent industries, then this might hasten the end of the trade. An anti-sugar pamphlet by William Fox was published in 1791; it ran to 25 editions and sold 70,000 copies in four months. Spurred on by pamphlets and posters, by 1792, about 400,000 people in Britain were boycotting slave-grown sugar. Some people managed without, others used sugar from the East Indies, where it was produced by free labour.
Grocers reported sugar sales dropping by over a third, in several parts of the country, over just a few months. During a two-year period, the sale of sugar from India increased ten-fold (see Adam Hochschild: Bury the chains). James Wright, a Quaker and merchant of Haverhill, Suffolk, advertised in the General Evening Post on March 6th, 1792, to his customers that he would no longer be selling sugar. He declared:
".....Being Impressed with a sense of the unparalleled suffering of our fellow creatures, the African slaves in the West India Islands.....with an apprehension, that while I am dealer in that article, which appears to be principal support of the slave trade, I am encouraging slavery, I take this method of informing my customer that I mean to discontinue selling the article of sugar when I have disposed of the stock I have on hand, till I can procure it through channels less contaminated, more unconnected with slavery, less polluted with human blood......"
(A full copy of this article can be read here)
The boycott was revived in the 1820s, as the English movement pushed for the total abolition of slavery in the British colonies. Abolitionists also campaigned for people to stop purchasing at shops that sold sugar produced using enslaved labour and some traders used notices - similar to the fair trade notices of today - to let customers know that their sugar did not involve slave-labour.
These campaigns were primarily supported by the female anti-slavery associations, who distributed thousands of pamphlets and leaflets door-to-door, in an effort to persuade British consumers not to buy West Indian sugar. English ceramic manufacturers responded by making sugar bowls and tea sets inscribed with anti-slavery slogans.
Although the effect may not have been crippling to the industry, it brought together abolitionists in common cause and, at a time when only a small fraction of the population could vote, citizens (particularly women) found the power to act when Parliament did not.
Below is a copy of William Cowper's poem concerning the slave trade and the link to sugar and rum.