In 1805 the House of Commons passed a bill that made it unlawful for any British subject to capture and transport slaves,
but the measure was blocked by the House of Lords.
In February 1806, Lord Grenville formed a Whig administration. Grenville and his Foreign Secretary, Charles Fox, were strong
opponents of the slave trade. Fox and William Wilberforce led the campaign in the House of Commons, whereas Grenville had
the task of persuading the House of Lords to accept the measure.
Greenville made a passionate speech where he argued that the trade was "contrary to the principles of justice, humanity and
sound policy"; and criticised fellow members for "not having abolished the trade long ago". When the vote was taken the Abolition
of the Slave Trade bill was passed in the House of Lords by 41 votes to 20. In the House of Commons it was carried by 114
to 15 and it become law on 25th March, 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 and Thomas Fowell Buxton, argued that the only
way to end the suffering of the slaves was to make slavery illegal. However, it was not until 1833 that Parliament passed
the Slavery Abolition Act.