The BBC’s Line of Duty accelerates to a cliffhanging crunch on Thursday night. The latest season of Jed Mercurio’s drama has showed no reticence about roping in police misdemeanours and cover-ups from the past.

The entire three-season plotline, revolving around fictional gangland boss Tommy Hunter, has already morphed into a story about historic child abuse, and may now head in the direction of political corruption itself. We already know the scandal involves a senior local politician, a police chief, a children’s home and – clearly shown in a photograph but not named – Jimmy Savile.

The sudden emergence of reality into a narrative that had been constructed as fictional prompts the question: why was the policing of the 1970s and 80s so bad that we are still, at the other end of a lifetime, haunted by it?

The short answer is: the wars. Three separate but overlapping conflicts shaped policing in the Callaghan and Thatcher eras: Northern Ireland, the cold war and the class war that Thatcher unleashed. The Irish war led to a string of torture cases, extrajudicial killings and miscarriages of justice, only some of which have been recognised to date. The atmosphere of renewed cold war after the Soviet invasion of Afghanistan, and the mass movement against cruise missiles, focused police efforts firmly on to the political left and trade union rank and file in Britain.

And the methods, attitudes and implicit permissions evolved in policing the external threats clearly spilled over into policing what Thatcher termed “the enemy within”. This, in turn, polluted the criminal justice system so badly that, if you found yourself accidentally on the wrong side of the machine – even at a football match – justice became elusive.

In 1984, five years before South Yorkshire police presided over the Hillsborough disaster, the same force had co-ordinated a quasi-military police operation against miners picketing the Orgreave coking works.

We know, because of cabinet papers since released, that the Conservative government’s claim – that the miners’ strike was policed neutrally – was false. Pressure was placed on home secretary Leon Brittan to intensify police measures in the early days of the strike, despite official claims of non-interference. Cabinet minutes record Margaret Thatcher saying it was “essential to stiffen the resolve of chief constables to ensure that they fulfilled their duty to uphold the law”. The result was mass arrests, unwarranted police violence, infringements on civil liberties and the historic confrontation at Orgreave.

The Orgreave Truth and Justice Campaign has collected extensive testimony alleging police fabrication of evidence, violence against people in custody and collusion. Ninety-five men charged with violent offences at Orgreave that day had their charges dropped after the prosecution withdrew police statements, many of which were identical. Police then paid out £425,000 in compensation to those wrongfully arrested.

Home secretary Theresa May is currently considering the Orgreave campaign’s demand for a full public inquiry into the policing of the 1984 mass picket. A separate statutory inquiry is under way into historical child abuse, including police handling of allegations and potential political links. Meanwhile, the National Crime Agency’s investigation into corruption allegations surrounding the Stephen Lawrence case is ongoing.

Today, after the Macpherson reforms to the Met, and the policing revolution begun after the Police and Criminal Evidence Act (1984), the areas for concern are different.

There is, we are assured, no more infiltration along the lines that led numerous female leftwing activists to be duped into relationships with undercover cops. There can be, we are assured, no repeat of overlap between policing and organised crime that has led to the NCA’s inquiry into the Lawrence investigation.

Yet organised crime today is, in so far as it can be estimated, arguably bigger than in the 1980s: higher than £24bn a year, according to National Criminal Intelligence Service, with “hundreds of billions of dollars” being laundered through UK banks.

The risks arising from the close proximity of a poorly regulated financial system, offshore tax havens, organised crime andmainstream politics are painfully obvious. So are the low number of prosecutions and even lower number of convictions for organised crime and corruption, compared to the multi-billion pound economic loss.

The unanswered question from the 1980s is: how extensive was the secret state, and how much of what is currently hidden from public view on grounds of “intelligence” would, if revealed, explain the pervasiveness of police malpractice in that decade?

Only once we know that can we take an enlightened decision about whether the current checks and balances – which should allow police and security services to operate within the law, against the real and present dangers that surround us – are adequate to keep the kind of scenarios depicted in Line of Duty to the realm of fiction today.