It's 9.11am on September 18 and a doctor is visiting a sick patient in Canterbury when an air-raid siren sounds.

A single-megaton nuclear missile has just overshot Manston airfield and burst six miles from this position, turning the county into a dead zone. The year is 1965 and this is The War Game.

Fifty-five years ago a trailblazing film director named Peter Watkins created a powerful docu-drama foretelling a fictional Soviet nuclear attack on Kent .

It was set against the backdrop of the Cold War as heated exchanges between the competing superpowers of the US and the Soviet Union threatened to push the world to the brink of nuclear devastation.

The film was shot on location in the towns of Chatham , Gravesend , Dover and Tonbridge with a budget of £7,000 and a 350-strong cast composed entirely of amateur actors sourced from local theatre groups.

Throughout, Mr Watkins uses a newsreel-style narrative and voice over to alarm viewers as to the nation's current preparedness (or lack of) for nuclear conflict.

Catastrophic events are depicted as plausible realities as the film seamlessly weaves between harrowing scenes of death and destruction in the quarantined town of Rochester .

There are also fictional interviews with official figures, including doctors and psychiatrists who offer a sobering reflection on the impact on the human mind.

However, its presentation of firestorms, radiation sickness and the lawlessness of police firing squads ultimately proved too much for its commissioners, the BBC, which shelved the flick.

Bosses claimed it would be "too horrifying for the medium of broadcasting" but would be shown to invited audiences, including those people who helped to make it.

But when it later emerged that prior to announcing its ban, the BBC had invited senior civil servants to a preview, it resulted in a backlash in public opinion. So outraged was Mr Watkins he resigned after claiming the broadcaster had violated its own charter of independence – an accusation it robustly denied.

Nevertheless the crisis and media attention that followed resulted in Labour MP Willie Hamilton tabling questions in the Commons to the Home Secretary as to whether it had interfered in the BBC's decision making.

It admitted officials had seen and commented on the picture but denied any involvement in the decision to pull it.

The BBC issued the following statement: “The BBC has decided that it will not broadcast The War Game, a film on the effects of nuclear war in Britain, produced by Peter Watkins. This is the BBC’s own decision. It has been taken after a good deal of thought and discussion but not as a result of outside pressure of any kind."

In a bizarre twist, the 46-minute film went on to enjoy a limited theatre release – buoyed by screenings from the Campaign for Nuclear Disarmament – and won an Oscar at the 1967 Academy Awards.

It would take until 1985 for it to eventually receive a TV audience when it was broadcast to mark the 40th anniversary of the strike on Hirsoshima and would be shown in schools and other educational settings.

But the public would have to wait even longer to find out more about the relationship between the State and the BBC in assessing the film's suitability for air.

Then in 2015, 50 years after it was first banned, Scottish academic John Cook, a professor at Glasgow Caledonian University, obtained previously classified Cabinet Office papers under a Freedom of Information request.

It detailed a lunch between the then head of the BBC Sir Hugh Greene and a senior minister where it was agreed the broadcaster would issue a press statement taking ownership of the decision should that be the "conclusion" reached.

Speaking at the time, Professor Cook said: “Examining the files, I was surprised at the level of scrutiny the government paid to the film and how explicit discussions were to suppress it. Politicians, not just civil servants, were involved, including then Prime Minister Harold Wilson.

“None of the discussions concerned preserving the independence of the corporation, but rather how to find a way to suppress the film without implicating the government or embarrassing the BBC. Much as we think we live in the era of political spin, the emphasis in the discussions was less on whether to censor but how best to present that censorship to the public.”

A BBC spokesman told The Herald in Scotland: "Fifty years on it's difficult for us to comment on the background to the broadcast of this programme."

Professor Cook discussed his findings as part of a special BBC Radio 4 programme aired the same year, which also included interviews with those involved in making the film.

In that show, late stunt co-ordinator Derek Ware described some of Mr Watkins' more unconventional methods.

He recounts how the director had arranged with the local council for a condemned row of houses to be saved so they could be set on fire as part of the film. The Dr Who stuntman described running around a burning building on his own and having to escape via a cupboard.

On another occasion he claims the police got involved after the director had initially failed to gain permission to shoot certain graphic scenes in the street.

Much of the filming of the post-strike devastation was shot at the Grand Shaft in Western Heights, Dover , whose semi-demolished barracks made for convincing nuke-damaged properties.

In gruesome scenes broadcasting the aftermath of the blast, children are seen crying with third-degree burns and clutching their eyes. Women are rendered infertile by the radiation.

Food riots are also depicted through violent confrontations between civilians and police in the streets. This ends in a priest reading the last rites before dissenters are put to death by firing squad.

In 2013, the BBC invited some of those who took part in the filming to watch the film, many for the first time, at a special screening inside a nuclear war bunker in Gravesend .

The Cold War bunker is in Woodlands park and was originally known as Civil Defence Region 6 when it was built in 1954.

Gravesend 's rescue and emergency services were to be co-ordinated in the event of a nuclear strike up until it was decommissioned in 1968.

Housewives from the riverside town featured in the production and were interviewed on their views as to whether the UK should retaliate in the event of a Soviet strike.

Mr Watkins recalls some of these conversations in a Q&A for a film-makers book with author Alan Rosenthal entitled "New Documentary in Action: Casebook in Film Making".

He spoke of how he took several cast members aside and explained to them he wanted to ask several questions and for them to say whatever they thought. The response, he says, was "they became simply lay members of the public" rather than actors.

It produced perhaps some of the most chilling scenes in the film as Mr Watkins sought to expose the common lack of public knowledge surrounding the nuclear debate itself.

Watkins, who went on to produce other films in self-imposed exile in France, no longer gives interviews on the film.

However, he explains the rationale behind it on his website: "In this film I was interested in breaking the illusion of media-produced ‘reality’.

"My question was - Where is ‘reality’? ... in the madness of statements by these artificially-lit establishment figures quoting the official doctrine of the day, or in the madness of the staged and fictional scenes from the rest of my film, which presented the consequences of their utterances?"

But ultimately his overriding concern and legacy was to help break the silence in the media on the nuclear arms race.

In doing so, Peter Watkins provided a cinematic space in which his audience was not only invited to see the issues the country faced but also to engage with and debate them.

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