Under the terms of the Abolition of the Slave Trade Act (1807) British captains who were caught continuing the trade were fined £100 for every slave found on board. However, this law did not stop the British slave trade. If slave-ships were in danger of being captured by the British navy, captains often reduced the fines they had to pay by ordering the slaves to be thrown into the sea.
Some people involved in the anti-slave trade campaign such as Thomas Clarkson, Granville Sharp and James Cropper, argued that the only way to end the suffering of the slaves was to make slavery illegal. William Wilberforce disagreed, he believed that at this time slaves were not ready to be granted their freedom. He pointed out in a pamphlet that he wrote in 1807 that: "It would be wrong to emancipate (the slaves). To grant freedom to them immediately, would be to insure not only their masters' ruin, but their own. They must (first) be trained and educated for freedom."
James Cropper remained concerned about the intentions of those who had opposed the anti-slave trade legislation. On 12th March 1822, he wrote to Thomas Clarkson noting that "on the abolition of the slave trade and the efforts of the British government to induce other governments to follow their example, there is some suspicion of a mixture of motive in the later part, nor can we wonder at it when we see the Assembly of Jamaica petitioning the King to use his influence to induce other countries to abolish it and at the same time petitioning against the introduction of East India sugar into this country."
In 1823 Cropper wrote to Zachary Macaulay suggesting the formation of a new abolition society. According to the author of The Great Abolition Sham: The True Story of the End of the British Slave Trade (2005): "Its strategy first and foremost would be to obtain information on the state of slavery in British and foreign colonies in the West Indies and in North and South America, in order to prove the argument that free labour was cheaper than slave labour but that the expense of cultivation would also be lessened by the amelioration of the hard treatment of slaves."
Later that year James Cropper, Thomas Clarkson, Samuel Romilly, Joseph Sturge, Thomas Fowell Buxton, William Allen, and Zachary Macaulay to form the Society for the Mitigation and Gradual Abolition of Slavery. Clarkson agreed to take to the road again to resurrect the old abolition network of some 70 local bodies and to establish new ones. Cropper offered Clarkson £500 to pay for the campaign.
In his book, The Great White Lie (1973), Jack Gratus argues that: "The plan was to divide the country into districts, and to send a lecturer to each, armed with facts and information about slavery and fired by an enthusiasm to convert new audiences around the country to emancipation. The Quakers accepted the idea immediately and Cropper advanced £500 out of his own pocket. The prosperous Birmingham Quaker, Joseph Sturge, who was to play such an important role in the later history of emancipation, advanced £250. Wilberforce gave £20 and James Stephen ten guineas."
Over the next few years Thomas Clarkson rode some 10,000 miles in his propaganda campaign. In 1825 women such as Elizabeth Pease, Anne Knight, Elizabeth Heyrick and Mary Lloyd began forming women's Anti-Slavery Societies. In 1824 Heyrick published her pamphlet Immediate not Gradual Abolition. In her pamphlet Heyrick argued passionately in favour of the immediate emancipation of the slaves in the British colonies. This differed from the official policy of the Anti-Slavery Society that believed in gradual abolition. The leadership of the organisation attempted to suppress information about the existence of this pamphlet and William Wilberforce gave out instructions for leaders of the movement not to speak at women's anti-slavery societies.
The Female Society for Birmingham had established a network of women's anti-slavery groups and Heyrick's pamphlet was distributed and discussed at meetings all over the country. In 1827 the Sheffield Female Society, became the first anti-slavery society in Britain to call for the immediate emancipation of slaves. Other women's groups quickly followed but attempts to persuade the leadership of the Anti-Slavery Society initially failed.
Henry Brougham was one of the main supporters of the Society for the Mitigation and Gradual Abolition of Slavery in Parliament. On 5th March 1828, Brougham argued in the House of Commons: "The progress of the colonies is so slow as to be imperceptible to all human eyes save their own. They are standing still instead of advancing towards the goal at which it was the wish of the House they should gradually but certainly arrive... Out of twenty heads of regulation and improvement recommended to them there was no less than nine in which not a single colony has not taken a single step. In Jamaica and Barbados with populations together of nearly half a million slaves not one step has been taken with respect to sixteen out of twenty heads proposed to them by the Colonial Department." Brougham complained that the Government had lamely replied that it was their desire "to introduce a system which will be beneficial to the slaves without infringing on the rights of private property".
In 1830, the Female Society for Birmingham submitted a resolution to the National Conference of the Anti-Slavery Society calling for the organisation to campaign for an immediate end to slavery in the British colonies. In an attempt to persuade the male leadership to change its mind on this issue, the society threatened to withdraw its funding of the organisation. The Female Society for Birmingham was one of the largest local society donors to central funds, and also had great influence over the network of ladies associations which supplied over a fifth of all donations.
The Society for the Mitigation and Gradual Abolition of Slavery continued to grow. In May 1830, 2,000 people packed the Freemasons' Hall to hear their leaders denounce the slave system. One member argued: "The friends of humanity have slept too long at their posts while the enemy never slackens his endeavours to perpetuate the present abuse by which his avarice is fostered. Indeed I fear that until some black O'Connell or an African Bolivar devotes his unceasing energy to effecting emancipation of his negro brethren, the condition of the slaves... will never change."
Henry Brougham, who was at the meeting, and had recently been given a peerage and had been appointed Lord Chancellor in Lord Grey's new Whig government, argued that Parliament was not ready to free the slaves in the colonies. Daniel O'Connell, who was also in Freemasons' Hall, challenged Brougham: "Let us make a beginning. Whatever day we propose we will be met with the answer, you are too hasty; you do not give enough time to educate the young descendants of slaves before they come to man's estate, and make them fit for freedom."
During the meeting the meeting the Society for the Mitigation and Gradual Abolition of Slavery agreed to drop the words "gradual abolition" from its title. Sarah Wedgwood suggested a plan for a new campaign to bring about immediate abolition. In 1831 James Cropper and his son-in-law, Joseph Sturge, formed the Young England Abolitionists, a pressure group within the Society for the Abolition of Slavery, that campaigned for a new act of Parliament. It was distinguished from other anti-slavery groups by its unconditional arguments and vigorous campaigning tactics. Peter Archer has argued that they directed "their activities much more in the direction of forming mass opinion."
The Anti-Slavery Society presented a petition to the House of Commons calling for the "immediate freeing of newborn children of slaves". Thomas Clarkson redoubled his efforts and between October 1830 and April 1831, 5,484 petitions calling for an end to slavery was sent to Parliament. However, Clarkson had to wait until 1833 before Parliament passed the Slavery Abolition Act that gave all slaves in the British Empire their freedom. It contained two controversial features: a transitional apprenticeship period and compensation to owners totalling £20,000,000.
James Cropper was disappointed by the measure that granted compensation to slave owners and substituting a temporary system of unpaid apprenticeship for slavery. Joseph Sturge visited the West Indies (November 1836 to April 1837) where he collected evidence to demonstrate the flaws in the legislation. On his return he published The West Indies in 1837 and gave evidence for seven days before a committee of the House of Commons. As a result of his campaign in 1838 the apprenticeship system was terminated.
On 29th March, 1838, Lord Brougham, argued in the House of Lords: "compulsory apprenticeship, which was another name for slavery, and could only be justified by expediency, is proved to be inexpedient, and nothing remains but the duty of the mother country to afford all her subjects the protection of equal laws." Jack Gratus, the author of The Great White Lie (1973) has commented: "With these strong words the highest legal authority in the land condemned fifty years of parliamentary inactivity under the guise of ameliorative legislation on behalf of the slaves, and condemned, moreover, the final act of hypocrisy for the fraud it was."