It was the stated aim of legendary Met commissioner Sir Robert Mark that his force should arrest more criminals than it employed. Thus we know that among the fine men and women who keep the capital safe, there have always been some bad ’uns.

But from more recent revelations, about secret operations against environmental protesters and even the family of Stephen Lawrence, we also know that the few bad apples theory didn’t and presumably doesn’t always hold. Sometimes Met officers behaved badly because the force told them to. Such malfeasance usually makes news, but last night it made for feisty period drama as Sky Atlantic embarked on Guerrilla, a six-part love story through which we learn something about the past activities of the secret Black Power Desk, a unit established by Scotland Yard in the 1970s.

This was a Special Branch initiative created on the specific principle that holds true today in many offices; that any gathering of more than two black people not subject to supervision can only mean trouble. Back then, keeping tabs on all those chips on all those shoulders was a difficult thing to achieve, because the Met had so few black officers that those it did employ were known to everybody. I recall a tale from my youth of one much-exploited black constable who slipped into a London house party in civvies scouting for drug offences. He was quickly outed. Down a corridor of stares, the interloper beat a hasty retreat.

He was a clodhopper in the wrong place in the wrong decade. But officers paraded in last night’s opener were of a different quality: steely-eyed, shameless, callous – and that was the best of them: chief inspector Pence, a predominantly mournful Rory Kinnear. He paid his black mistress/informant to find him a black activist nark willing to disrupt an otherwise peaceful protest so that disorder would ensue and his main quarry could be targeted. He showed the amped-up constables a photo of the target, but they were the ones who actually caved in the target’s head with their truncheons, murdering him in plain sight. And among them, presumably, was the constable who had earlier punched the deceased’s white Irish girlfriend in the mouth prior to very obviously sexually assaulting her during a illegal body search (a scene of law enforcement abuse lifted wholesale from the Oscar winning film Crash). So Pence/Kinnear was bad, but for hands-on thuggery, he wasn’t the worst. And sad to say, for those who recall this paranoid, unashamedly racist era of British policing, none of that would have seemed outlandish.

This was drama informed by social history, as opposed to social history told as drama. Writer and director John Ridley – of 12 Years A Slave – and executive producer Idris Elba were rightly keen to highlight a clearly neglected facet of recent history, but a bleeding heart never was sufficient to secure major production funding. So here is the political battle between minority communities and an hysterical establishment viewed through the prism of two romantically attached activists: Marcus, an unemployed black English teacher played by Babou Ceesay and Jas, a warrior queen nurse of Indian origin played by Freida Pinto.

It was largely Pinto’s show, a fact already raising hackles among a current cadre of activists who fear the role of black women in Britain’s Black Panther movement is being downplayed. Pinto took lead credit and drove all the significant events; plotting and masterminding the springing from Wormwood Scrubs of a charismatic black leader – templating a similar operation by Germany’s Baader-Meinhof group. She kept a cool head when Marcus – a clever guy who doesn’t, thus far, seem cut out for the renegade life – shoots a blameless emergency worker and seems ready to unravel.

Elba – as Kent, an old flame of Jas’s, too cerebral to advocate gun-toting and jail-breaking and therefore unsuitable boyfriend material – pops up sporting sideburns and the displaced performance wig of a 70s soul crooner, but the light is Pinto’s. She does spiky with gusto if not complete conviction. As battle intensifies, with the police unit, with Marcus and with her fellow activists, she promises to be awesome – or really quite irritating.

There’s a clamour, very justified, for more diversity on TV and this is clearly part of that. The weaving of a black experience into drama; the broadening of the canvas. But this show, part-financed by the US cable network Showtime, is very much for the mainstream; it isn’t arthouse, a Timepiece documentary or a campaigning exposé.

Sometimes, it is soap opera. Amid the furore of the jailbreak, Jas and Marcus seem surprised. “You’re soldiers now,” the escapee tells them. Jas throws up. Are we cool, Marcus asks her soon afterwards? Jas smiles and offers episode-closing reflection. “We are so fucking cool,” she says.

Some will wish for more gravitas. Maybe one of the other canvas broadening productions in gestation – Steve McQueen’s grand sweep black family drama for the BBC, for example – will lean that way. Guerrilla is what it is, and I’ll take it for that.