AT THE beginning of each episode of “Guerrilla”, a different quote appears on screen. All revolutionary in tone but unattributed, the quotes invite viewers to consider the words without preconceptions. “Those who protest injustice are people of true merit,” reads one. “Protest is when I say this does not please me. Resistance is when I ensure what does not please me occurs no more,” says another. After a few seconds, the author’s name is revealed—Ho Chi Minh in the first instance, Ulrike Meinhof in the second. It is a ploy that forces the viewer to reassess their convictions, demonstrating how fine the line can be between freedom fighter and terrorist.

Lines and labels, especially those imposed on the oppressed, are things that interest John Ridley. Best known for his Academy Award-winning screenplay for “12 Years a Slave”, Mr Ridley penned most of “Guerrilla” and directed three of the six episodes. The mini-series follows the radicalisation of a small group of left-leaning activists living in Brixton, south London, in the early 1970s. A mixed-race couple is at the heart of the group: Marcus (Babou Ceesay), a black, unemployed teacher who is turned away by recruiters who look longer at his skin than his resume, and Jas (Freida Pinto), a nurse whose activist father is imprisoned in India.

As “children of the colonised”, Jas and Marcus are enraged by the impending Immigration Act of 1971, real-life legislation that removed Commonwealth citizens’ automatic right to remain in Britain. “When you’re black and British there is a constant struggle to understand who you really are,” Marcus writes in a political pamphlet. “Strong in our pride, it’s only when we came to what we’d built we were forced to question who we really are: a citizen or a visitor?” After police bludgeon their friend to death during a protest in broad daylight, the couple decides to take “direct symbolic action” by freeing a political prisoner. Against the odds, their plot succeeds. Soon the “black power desk” in Scotland Yard, a unit tasked with crushing dissent, has printouts of their faces.

Set just three years after Enoch Powell’s “Rivers of Blood” speech, “Guerrilla” doesn’t turn away from this unabashedly racist era of British policing. The black power desk was a real unit, the vestige of an establishment clinging to the last remnants of empire. In the series, Pence (Rory Kinnear), the principal officer on the case, was raised in apartheid Rhodesia, and he manipulates, beats and bribes the black community, his tactics only growing more thuggish as the activists gain acclaim. But this is not a clear-cut tale of villainous police versus righteous activists. As time passes, we learn of Pence’s loveless marriage, drug-addled son and illegitimate child by his black mistress. It of course does not justify his methods, but it makes it easier to comprehend why he yearns for the “clean order” of Rhodesia.

The radicals, too, are not painted in a uniformly rosy hue. Violent acts have bloody consequences, even those in the service of a movement. Ostensibly fighting for the “unity of people of colour”, Mr Ridley depicts a scrappy movement divided by competing ideologies, egos and methods. The cohort bickers over plans to attack a travel agency. Should they merely deface the building, storm in with guns or blow it up?

Mr Ridley initially thought of setting “Guerrilla” in San Francisco, and at times the show feels like an American story shoehorned into a London setting. This is particularly true of the gun-toting and more extreme violence. The British Black Power movement was largely composed of grassroots organisation and community activism. That is a gentler, but equally fascinating, narrative.

In the end, “Guerrilla” is a dramatisation, rather than a definitive account, of the Black Power movement on the other side of the Atlantic. The legacy of colonialism and the struggles of immigrants who feel disenfranchised and diminished are themes that still feel vital. Where it works best is in its exposure of the pervasive institutional racism that is too frequently skipped over in the retelling of this period of history. It might be ugly and uncomfortable, but “Guerrilla” forces viewers to think about where the country once was, and where it now might be.

“Guerrilla” is available on Sky Atlantic in Britain and Showtime in America