That is somewhat misleading.
The English courts ruled that slavery had no legal basis in England at least as far back as Elizabeth I in 1569.
From that period forward, the number of "slaves" in England was probably less than 10,000.
In most cases, those "slaves" were indentured house servants brought into England from the Caribbean by people who worked in the plantation or slave trading business.
By the late 1700s, the English Quakers were working relentlessly to free all the Black indentured servants in England.
From memory, the slave legislation passed in 1833 simply forbade sending Black indentured servants back to the Caribbean, where they would become slaves again.
Anecdotally...
I have been watching Masterpiece Theatre and BBC programming for 50 years on my local PBS stations.
I do not recall ever seeing a program about slavery in England.
The Slavery Abolition Act of 1833 abolished slavery throughout the British Empire, with the exception of India, which was constitutionally complicated because the Indian States were nominally independent though under the thumb of the East India Company. Slavery had become rare in England itself by that time and took mostly the form of indentured servitude, but it still existed in the colonies, notably in the Caribbean. The 1833 Act was the great example of compensated emancipation, which was the road unfortunately not taken in the U.S. We found a much more expensive way to abolish slavery. In the U.S., compensated emancipation was done in the District of Columbia in 1862. Elsewhere it was done through a mix of wartime self-emancipation, the Emancipation Proclamation, and Union bayonets, all ratified and regularized eventually by the 13th Amendment. The last place in the U.S. where large scale chattel slavery existed legally was actually Kentucky, which did not secede and was therefore a Union state not covered by the Emancipation Proclamation. Kentucky newspapers were still running ads for slave auctions when Lee was surrendering at Appomattox. Slavery in Kentucky only ended with the 13th amendment.
You didnt need to be an African slave to be human chattel for the English
Ask the Irish
and the lower classes in England sent to work houses or transported to Australia or the colonies for debt or minor crimes like stealing food or game