Previously unseen footage in a Channel 4 documentary about the Battle of Orgreave was confirmation if any was needed that heavy handed policing of a mass picket outside the Orgreave coke works in June 1984 descended into unprecedented brutality.

Battered and bloodied pickets were captured on camera by two officials from the National Union of Mineworkers who carried on filming amid the mayhem – footage that had been left for years locked in a cupboard and which was broadcast for the first time.

Hanging loose among scenes of blood and gore were unanswered questions: why did Monday 18 June 1984 become the “bloodiest day” of the 1984-85 miners’ strike? Why was it the pivotal event in the “largest police operation in British history”?

Survivors of a confrontation that was akin to a medieval battle retold their story in The Miners’ Strike 1984: The Battle of Britain and then described their relief when a 48-day trial collapsed, and 95 pickets were acquitted of charges of riot and violent disorder.

Two of the men’s lawyers Gareth Pierce and Michael Mansfield described their disbelief at the mass fabrication of police statements and a catalogue of errors and stupidity which had left the chief prosecutor with no option but to capitulate.

Given the overwhelming evidence that it was the police who were the aggressors and not the pickets, the raw testimony of men who were there that day, and who went through the trial, will not only stand the test of time but will also continue to raise nagging questions as to why Orgreave became such an infamous flashpoint.

Early on in the documentary there were one or two clues as to why a force of 3,000 officers had been assembled from across the country to confront 6,000 pickets at Orgreave.

From the start of the strike, the NUM President, Arthur Scargill, had wanted to force the closure of the coke works but initially he was overruled by the union’s executive. Finally, the word went out to local union offices, miners’ clubs, and soup kitchens: the mass picket at Orgreave 18 June was a priority.

The two NUM officials who had been issued with video cameras described what they saw that day and posed questions that were not followed through: Why were the police there in such strength? Who alerted the television crews?

When the National Coal Board and the government were first alerted that Orgreave might become a target the alarm bells had rung.

There was no way that Prime Minister Margaret Thatcher was going to allow Scargill to repeat his 1972 victory when a mass picket closed the Saltley coke works at Birmingham and forced her predecessor Ted Heath to concede a 27 per cent pay rise to the NUM.

Winning “The Battle of Saltley Gate” was – as Scargill has frequently said --   the proudest moment of his life but was acknowledged within the government as a disaster when it came to policing industrial unrest; furthermore, it was a retreat that was seared into the political memory of the Conservative Party.

Although at the time he was a lowly organiser and activist in the mighty Yorkshire NUM, Scargill had seized the initiative and mobilised pickets from local pits to head south for Birmingham and, together with other trade unionists from neighbouring car factories and engineering works, a force of 800 police officer found itself far outnumbered by 30,000 protestors.

Sir Derrick Capper, head of the Birmingham force, ordered the coking plant to close its gates “in the interests of public safety” and Scargill was handed a loud hailer to ask everyone to disperse.

Flying pickets, as they came to be known, were soon a formidable presence at many of the bitter industrial disputes of the late 1970s and early 1980s.

Such was the consternation after the humiliating events at Saltley that the Association of Chief Police Officers established the national reporting centre with the authority to deploy officers from police forces across the country in the face of exceptional threats to public order.

Within the first week of the 1984 strike Mrs Thatcher issued an edict to chief constables to “stiffen their resolve” because she was deeply disturbed by the speed with which Scargill had resorted to unlawful mass picketing and she feared the NUM leader was about to repeat his 1972 victory in Birmingham.

Days after her intervention the police began turning back flying pickets from Yorkshire who were heading south on motorways towards the Nottinghamshire and Midlands coalfields, and pickets from Kent heading north through the Dartford tunnel – this was the first highly visible sign of the co-ordinated response that would result in 18 police forces sending officers to Orgreave.

When her cabinet papers were released in 2014 under the 30-year rule Mrs Thatcher’s micro-management of the dispute was revealed: the South Yorkshire force was given secret authorisation to go on incurring the additional cost of bringing in police reinforcements to Orgreave.

She told the Home Office to give the South Yorkshire force “every support”; in the corner of one document was her hand-written note asking: “Can we provide the funds direct?”

One document which also caught my eye among the many official papers was from the Department of Energy, dated 5 June 1984, which notified the Chief Constable of South Yorkshire that British Steel wanted to clear the remaining 8,000 tons of coke from Orgreave to Scunthorpe by road in the week commencing Monday 18 June – they very day that Scargill had chosen for the mass picket.

The police action needed to be “part of a carefully conceived and well executed operation” … “to minimise any opportunity for the NUM to claim a victory.”

The timing of this government intervention helped to explain why so many police reinforcements were present on 18 June.

Convoys of lorries started taking coke from Orgreave to the Scunthorpe steelworks on 25 May and as the picketing intensified police used riot gear and mounted police for the first time on 29 May; the following day Scargill was arrested for obstruction.

By informing South Yorkshire police on 5 June of that the final clearance of coke from Orgreave would commence on 18 June, the Department of Energy had given the national reporting centre ample time to organise additional support from forces around the country.

There had already been a taste of what was to come at the dress rehearsal on 29 May when South Yorkshire said 41 officers were injured, 28 pickets hurt and 82 arrested.

Sophisticated police surveillance during the strike – including the extensive use of phone tapping – would undoubtedly have picked up news of the NUM’s plan to make Orgreave the focus for picketing on 18 June.

The two NUM officials explained why Scargill had wanted to picket Orgreave from day one. His theory was that if the NUM could stop coke being moved to Scunthorpe it would close the steel works, halt production at other plants and force negotiations that would “resolve the dispute”.

Scargill had made no secret of his intentions when calling for support: “I am asking my members to picket Orgreave in massive numbers to show we are not going to allow them to smash the miners’ strike.”

While tv news bulletins concentrated on the violent scenes that unfolded – and especially the charges by mounted police and officers with riot shields and batons drawn – the front pages of next day’s newspapers were filled with photographs of a bruised and battered Scargill being led away by police, apparently after having fallen over, having tripped over a chain link fence, and hitting his head on a railway sleeper. He spent the night in hospital.

A week later I was able to ask Scargill what happened. He said the police had changed their story three times as to why he had fallen over. As to the conduct of the mass picket, he said he had been in charge at Orgreave throughout the day, maintaining contact with the lead pickets by walkie-talkie radio.

In later years, when reflecting on the strike, Scargill did not hide his disappointment at his failure to repeat his success at Saltley. He had wanted the mass picketing to resume at Orgreave next day believing the police would not have been able to call in so many reinforcements.

Strike organisers in Yorkshire overruled him once again and their pickets returned to the Nottinghamshire coalfield determined to keep up the pressure on working miners to join the strike.

Such was his belief in the invincibility of the brute force of mass picketing, he seemed convinced that it would have been possible to “finish it off” at Saltley, if only they had returned next day.

To my surprise he told me he thought Mrs Thatcher would have played it just the same as he had if she had been leader of the NUM.  He was convinced she would have realised the political significance of a defeat at Orgreave that matched the Conservatives’ humiliation at Saltley.

Orgreave was a turning point: the police had gained the upper hand and from then on, the police operation was one of containment.

History was not to be repeated. Surprise tactics, the mass movement of flying pickets and sheer strength of numbers had failed to deliver the knockout blow that Scargill believed was possible.

The shock troops of the British trade union movement would not give in. Picketing continued throughout the summer and on into autumn and winter but support for the strike ebbed away as the return to work gathered pace allowing Mrs Thatcher to declare victory early in 1985 when she claimed half the men were back at their pits.

Events at Orgreave remain a stain on British policing. Repeated demands by the Orgreave Truth and Justice Campaign for a public inquiry have been refused. In 2016 the then Home Secretary, Amber Rudd, said there would no statutory inquiry or independent review, and according to the most recent statement from the Home Office that remains the position.

Campaigners hope that might change if events and publicity during the coming year of the 40th anniversary of the strike – with more documentaries and debates to come -- can generate an upsurge in public interest and a repeat of the demands for action that have followed in the wake of the ITV drama Mr Bates vs The Post Office.