The Regency Period was in the first quarter of the 19th century. Any blacks in England at that time were probably slaves. Slavery wasn’t abolished in England until 1833, after the Regency period was over.
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.
Blacks only started coming to Britain en masse after WWII with the Jamaicans, they needed workers after the war to make up for the manpower shortage the war left.