When the “triangular trade” began, manufactured goods went from Bristol, Liverpool and London to the African coast, where textiles and guns were bartered for black slaves. The slaves were taken across the Atlantic to the Leeward Islands, Surinam and Jamaica, and there exchanged for sugar, spices and rum. These goods were then brought back - on the third leg of the “triangle” — to Britain, and sold.
It was an enormously profitable trade — one product of which was the creation of black communities in the slave port towns, as slaves and black sailors found their way to Britain.
By 1800 the black population of Britain was probably around 10,000, from a general population of 9 million.
The first black political leader in Britain was Olaudah Equiano who was kidnapped by slave traders as a child. By saving from petty trading he bought his own freedom for £40. Equiano travelled widely; in Britain he participated in the — largely white — abolitionist movement, wrote a key, popular expose of the slave trade, Interesting Narrative, and joined the radical London Corresponding Society.
One of the five poor and determined radicals hung after the “Cato Street” conspiracy, in 1820, was a black man, William Davidson. A black tailor, William Cuffay, was a hero and martyr of the Chartist movement — transported with two white comrades to Tasmania in 1849 he died there, in a workhouse, in 1870.
The British slave trade was only abolished in 1807; slavery itself in 1833. Racism, which had developed as a justification for slavery, continued, expanded and mutated to justify Empire. Peter Fryer writes, “From the 1840s to the 1940s Britain's ‘native policy' was dominated by racism. The golden age of British Empire was the golden age of British racism too… the flood-tide of racism never completely submerges the image of black as ‘man and brother'... kept alive by three distinct traditions: humanitarian abolitionism; radicalism; and working class solidarity."
Indeed, there has been a strong tradition of white racism in Britain, but there is also a strong current of anti-racism and solidarity, too. For example, during the US civil war (1861-5), the British government was sympathetic to the slave-owning Southern states. The British workers were generally for the North and abolition (Karl Marx, for example, reports on attending large workers' meetings called to back the Northern states), and even at great cost to themselves: the workers of old Chartist centres of north-west England suffered tremendous hardships because the North was blockading the slave ports and stopping the flow of cotton to the British textile industry. But they stood solid “for Lincoln and liberty”!