Racism isn't static. The way individuals have perceived race and 'the other' has always been in continuous motion and change. The way a Londoner in the 16th, 17th, 18th, 19th, and 20th century perceived of a person of African descent have never been the same. Racialized concepts of men and women of African descent were shaped by a multitude of different factors over the centuries which included matters such as religion, colonialism, the slave trade, abolitionism, exoticism, and science. Sometimes, two different images could exist at the same time. This is the case we now face as we look into the perception of men and women of African descent between 1827 and 1830.
As always when we ask questions about history, we should consider a primary source. In this case, I want the reader to take a look at the following image. It is a design of an anti-slavery medallion, designed and produced in large numbers by British abolitionist Josiah Wedgwood in 1787. The medallion was originally made out of ceramic for the Society for the Abolition of the Slave Trade and was very widespread. This is not particularly surprising since abolitionism was becoming increasingly popular in the late 18th century. The anti-slavery movement, starting with the opposition against the slave trade in general (which was abolished in 1807) and later slavery in the British Empire, crossed social and economic boundaries to gain a genuine national support in Great Britain. As historian James Epstein writes: "Judging from subscription lists, from the wide support for consumer boycotts of West Indian sugar and rum and from anti-slavery petitions, anti-slavery mobilised extraordinarily large numbers."
Through this popularity, individual abolitionist and societies like the Society for the Abolition of the Slave Trade were instrumental in shaping a new image of people of African descent that stood in opposition to the previously established image of African slaves as produced by slave-owners and planters in the British West Indies: the racial myth of "Quashee". "Quashee" was the representative West Indian slave in the planter's imagination. Catherine Hall writes that "Quashee" was characterized as "lazy, mendacious, incapable of working without the whip, mentally inferior and sexually depraved." This is perhaps the way that we in the 21st century imagine that the average Londoner would have perceived of a man of African descent in the early 19th century. Yet, the popularity of the anti-slavery movement in Great Britain was moving towards its highest achievement in the late 1820s: the abolition of slavery in the British Empire, something it would achieve in 1833. As Epstein writes, the abolition of slavery in 1833 became "a hallmark of British national identity: as a nation, Britain was redeemed by an act of disinterested, Christian benevolence." The campaign to reach this point needed to create a more sympathetic image of the person of African descent and this is where we return to Wedgwood's design.
"Am I not a man and a brother?" asks the enslaved man on his knees depicted on the medallion, his hands clasping together as if praying, the symbols of slavery visible on his semi-nude body. In this figure, Wedgwood creates a westernized depiction of an African slave that makes an attempt to humanize him in an appeal for the viewer to consider him an equal. What we instead see is the creation of a different racial myth, that of a meek victim of "white oppression, grateful to their savior, ready to be improved and transformed." He is a Christian, westernized man of African descent who waits on his white saviors and appeals to them through the use of biblical language. This became the image that abolitionists spread to gain sympathy for the plights of slaves in the West Indies. Due to the widespread popularity of the movement, the image became entrenched in the popular perception of the British people and remained dominant until the 1840s.
The social and economic difficulties that the British colonies in the West Indies in the late 1830s and 1840s set the groundwork for a new racism, championed by men like Thomas Carlyle, that returned to the planter's image of the racially inferior African as a way to explain the downturn of British West Indies colonies after the abolishment of slavery. This would develop in the following decades into a new strain of virulent popular racism in combination with the rise of scientific racism, creating new racial myths for the Victorian era.
To summarize: Between 1827 and 1830, the perception of a black British man would most likely be that of a condescending, racial myth. Seeing as the character in question is a policeman, he would be considered within that racial myth and stereotype as a responsible, Christian man who proves that holding a man in bondage is wrong and immoral. He is, in the abolitionist mind, the "improved and transformed" man.
Sources:
At Home with the Empire: Metropolitan Culture and the Imperial World by Catherine Hall and Sonya O. Rose (ed.) (Cambridge University Press, 2006).
The Lords of Humankind Re-Visited by Catherine Hall in Bulletin of the School of Oriental and African Studies, University of London, Vol. 66, No. 3 (2003), pp. 472-485
The Wedgwood Slave Medallion: Values in Eighteenth-Century Design by Mary Guyatt in Journal of Design History, Vol. 13, No. 2 (2000), pp. 93-105.
There is known to have been one black policeman in England, John Kent, serving in Carlisle (the county town nearest the Lake District, not near major conurbations, and not known for its diversity) from 1837-44. (There does not appear to have been another until Norwell Roberts in the London Met in the 1960s.) The records about John Kent were discovered only in 2006 - so Roberts and those around him during his career had always considered him the first - and the books I’ve been able to consult were written before that, so the only sources I can link are newspaper and similar articles about the discovery.) John Kent was the son of Thomas Kent, brought to England as a servant from the Caribbean by a colonial landowner who also had property in Cumberland. Thomas chose the surname Kent after the English county where the ship landed. He later married a local white woman in Carlisle and had children. John Kent had a number of jobs during his long life, all in the Carlisle area, though an obituary in a local paper (image of part of it in this news article ) portraying him as a notable local character, noted his time in the police and that his nickname “Black Kent” had been used to scare naughty children– although Kent himself was actually a friendly person. He was dismissed from the police for drunkenness, and prior to that had had a couple of warnings for lateness. The Cumbrian policeman / local historian who discovered the records while writing a book on the history of the force contextualised the drunkenness as common among police constables of the time, because the quality of the water in the town was poor, making it safer to drink alcohol.
I don’t have access to a highly relevant book, Black London: Life Before Emancipation by Gretchen Holbrook Gerzina, and I’m only looking at the Amazon preview of the recent Black and British by David Olusoga, among the titles which would ideally be consulted for this topic. (Olusoga has also presented a short documentary series by the same name, which OP may be interested in having a look at.)
Alongside the widespread iconography of pitiable slaves appealing to white benefactors, which has already been described by u/Bernardito, there were some more positive representations, such as those mentioned in the introduction to Olusoga’s Black and British. One is a brass relief from the base of national monument Nelson’s Column, constructed 1840-43. (N.B. The Abolition Act, as applicable to slavery in the Caribbean, had been passed in 1833.)
The admiral lies mortally wounded in the arms of his men and fellow officers. To the left stands a black sailor holding a musket. His head is tilted upwards as he scans the rigging of the enemy ships. The man’s features are unmistakably and unambiguously African. Not only was this black seaman including in the relief, which was cast 35 years after the battle, he was both acknowledged and celebrated. When the reliefs were unveiled one contemporary reviewer was particularly drawn to what he called ‘the figure of the negro’ whom he described as ‘a perfect work of art - full of character, the distended nostrils, strained eye-balls and the firm manner in which the gun is clasped in his hand, clearly tell the emotions which might be supposed to occupy the mind under such circumstances.’ There was no suggestion in this effusive review, written near the high watermark of British anti-slavery sentiment, that the mind of this black sailor might be inferior to those of his white comrades, or that the emotions that surged in his heart during the heat of battle might be less noble than those of Europeans.
Before abolition, there were many political cartoons that stereotyped enslaved black people, more often as sympathetic and helpless victims, occasionally as ignorant or lazy. Myers notes that 18th satirical artist William Hogarth made more integrated portrayals of black people living among the poor and in other settings in London, which have been studied by David Dabydeen. Some examples from Hogarth, and other 18th century art including individual portraiture, here
In late 18th century London, there are estimated to have been around 10 000 black people.
Fryer noted in a chapter about the years 1787-1833 that most Black British people whose names are known from this period were political activists or prize-fighters, seeing this as an indicator of how tough life was. Myers (1996) stated that the majority of black people in London were poor and illiterate. (Many poor white people were also illiterate.) The commonest occupation was domestic service; she also notes records of lascars (sailors from the Indian subcontinent), beggars, criminals (known about because of surviving court records), and that black bandsmen were found in a number of army regiments from the 18th century. In the first two decades of the C19th, people of unusual appearance, such as albino black people and the San woman Saartje Bartmann were still being brought to Britain to be exhibited as freakshows. A small number of educated black people became known in society and were in certain ways important for the emancipation cause, but could also be seen as special exceptions to an otherwise stereotyped majority: C18th writers Olaudah Equiano and Ignatius Sancho – the improved men as described in the previous answer (expected to live up to higher standards of behaviour than would a white man born to rank), or who could be seen as essentially different where convenient. A further intriguing example, mentioned by Sandhu (1997) whilst reviewing Myers and Gerzina, was "Pablo Fanque (a.k.a. William Darby), the acrobat and North of England circus proprietor."
It was money that made a difference to the social standing of some individual black people, Fryer considers:
In 1805 a black man able to afford fashionable clothes could walk along Oxford Street arm in arm with a well-dressed white woman, unmolested and relatively unremarked – except by a surprised and primly disapproving white American visitor.
In that decade “men of colour in the rank of gentlemen” were first remarked upon as a sign of social change by one woman diarist he quotes, who also mentioned seeing a well-dressed black lady and her somewhat lighter-skinned children at the opera.
As an example of the barriers to employment for the potentially middle class, a reference for a Gloucestershire teacher in 1815 states “where so dark a complexion is not objected to, he would make a very valuable schoolmaster”.
Myers in 1996 found it unclear to what extent there was a black community in Regency London, versus a general tendency to assimilate. Olusoga also notes the assimilation, and that many of the first well-known black people were black men who married white women, and whose later descendants are probably unaware of their origins. This went on in practice regardless of the disapproval of sections of society, even from some abolitionists such as William Cobbett. At a dinner chaired by William Wilberforce in 1816, the African and Asian attendees, representative of the groups cause, were expected to dine separately, behind a screen.
While making less of an issue of the character’s skin colour in London than would happen in the USA at the same time is accurate, having him go about his work without any questionable nicknames or experiences of exclusion unfortunately seems very unlikely. (Yet of course, there is no reason why a fictional fantasy series should be expected to adhere to absolute historical reality; it is its job to portray a somewhat different world. And I understand this series and this character is probably also paying homage to another more recent – written - series.)
References
Peter Fryer, Staying Power: The History of Black People in Britain (2nd ed 2010, first published 1984)
Norma Myers, Reconstructing the Black Past: Blacks in Britain 1780-1830 (1996)
David Olusoga, Black and British: a Forgotten History (2016)
Sukhdev Sandhu, ‘At the Hop’, London Review of Books (1997), [Review of Black England: Life before Emancipation by Gretchen Gerzina and Reconstructing the Black Past: Blacks in Britain 1780-1830 by Norma Myers].
Articles about John Kent:
https://cumbriaguide.co.uk/carlisles-john-kent-was-uks-first-black-policeman/
Both /u/Bernadito and /u/Vespertine have provided good answers, with solid bibliographies that I heartily endorse. They make the broad points that (a) people of African descent have lived in Britain since the early modern period (at least Tudor times if not earlier), and that (b) racial attitudes toward Africans have changed considerably.
Another example that also points to the broad plausibility of non-white individuals functioning effectively in British society is the case of Dean Mahomet. A descendant of the Persian-speaking, Muslim, Mughal administrative class, he was born in the mid-18th century Patna, a north Indian city. At age 11, he attached himself to an Anglo-Irish officer in the East India Company's Bengal Army, and marched around with them, eventually becoming a sublatern officer, for 15 years. At the end of that time, he moved, with his officer-patron, to Cork, Ireland, where he lived for twenty-five years. He married an Anglo-Irish woman (and seems to have converted to Christianity, since his children were baptized in Anglican churches), and seems to have integrated himself into Anglo-Irish society perfectly fine. In the early 19th century, after some changes in family fortunes, he relocated to London, where he opened a "Hindustanee Coffee Shop" that was really a curry restaurant. It did fairly well for a few years but then failed as it couldn't establish a permanent clientele among London's elites (most of whom had their own kitchen staffs). He then moved to Brighton, where he ran a kind of "Oriental" bathhouse for another 25-some years. During this time, he bathed two different Kings of England, and was by all accounts a prominent member of Brighton's commercial society. His businesses declined and he died in pretty modest situation in 1851.
Several elements are worth noting here: first, as I noted for his time in Ireland, he married an Anglo-Irish woman of aristocratic background, and there appears to have been no opposition on grounds of racial or ethnic mixing. Second, his children seem to have integrated into British society just fine; one of them was a career postman, and another a published author. Again, there's no evidence of explicit racism against them.
All that said, it should be noted that the way he survived in Britain in the late 18th and early 19th century was by explicitly marketing his foreignness: that was the appeal of his restaurant and of his bathhouse. He published a memoir of his service with the Bengal army in the late 18th century, and then later essentially invented a story of medical training in India to make his bathhouse seem both exotic and medicinal. (This was well within normal practice at the time though, so quack-ish as it may seem to us, it was common.) And, his foreignness was protean and "Orientalist" in the Edward Said-ian sense: it collapsed all elements of a great, mysterious, ancient, sometimes decadent "East" into one master category of not-Europe, or not-British. So, his coffee shop is apparently "Hindu," but he was himself Muslim (and then apparently Christian). His bath house touted the wonders of Asia, and used Turkish, Persian, South Asian, and East Asian motifs.
So, Mahomet shows us that it was absolutely possible to live in Britain as a non-white person in the first half of the 19th century, and, provided one had some money, live as well as any other person. He also shows us, though, the awkward contradictions one might find oneself in by living that way: he was "foreign" in that he was from India, but "British" in that he lived more of his life in the Archipelago of the North Atlantic. He was "Indian" in that he was from India--or what would become India--but had to play a certain kind of "Indian" to survive commercially. Now, maybe he didn't HAVE to do that; he probably could have found other ways to make a living. But it is what he did all the same.
Finally, as others have pointed out, Britain's racial attitudes changed and hardened considerably after the mid-19th century. Emancipated slaves in Jamaica didn't always do what British plantation owners wanted them to; the Morant Bay Rebellion in 1867 changed some British minds about the status of Africans. Similarly, the Indian Rebellion in 1857 (sometimes called the Sepoy Mutiny) also changed plenty of British minds about the racial status of people in India. These developments, plus the development of scientific racism and a more authoritarian, conquest-oriented imperial culture developed in the late 19th century. By then, it's harder to imagine people of color living relatively "normal" lives in British society--even if their numbers actually in Britain were increasing.
Dean Mahomet's own Travels, his account of his years with the Bengal Army, is edited by Michael Fisher and includes some excellent supplementary scholarship on both South Asia in Mahomet's time, and on his later lives in Ireland and Britain. It's published as The Travels of Dean Mahomet, ed. Michael Fisher (1997).
For the evolution of racial attitudes in Britain in the 19th century, THE key work is Catherine Hall's Civilising Subjects (2002).
