Secret files reveal BBC colluded with Whitehall to ban its own nuclear war film

The corporation insisted it was its own decision to implement the ban as the footage was "too horrifying for the medium of broadcasting".

However the move has been mired in controversy ever since, as it was known the drama had been viewed by Whitehall officials in the weeks beforehand.

Now fifty years on, John Cook, professor of media at Glasgow Caledonian University, has uncovered previously secret Cabinet Office files which show how civil servants influenced the banning of the film. His findings will be discussed as part of a BBC Radio 4 programme 'The War Game Files', which will be broadcast on Saturday 6th June at 8pm.

In an interview with the Sunday Herald Cook said: "This has been a 50 year mystery - I wouldn't say I have solved it, but it is probably the closest we have got to figuring out what happened.

"The BBC put out a press release in November 1965 saying they had decided not to show the film to the public as it was too horrific for the medium of broadcasting - and stressed it was a decision the BBC had taken alone.

"But there has been much suspicion over the years that the British Government was involved in the censorship in one form or another."

Sir Norman Brook, who was chair of the BBC Board of Governors at the time - and whose previous job as secretary of the Cabinet Office included drawing up civil defence planning in case of a nuclear war - had written to Cabinet Secretary Sir Burke Trend to alert him to the film ahead of its planned broadcast.

Cook said one key memo he uncovered revealed Brook and Trend subsequently had a meeting with then director of the BBC Sir Hugh Carleton Greene.

He said: "In the memo Sir Hugh Carleton Greene said if it was decided by the government the film should not be shown, then the BBC would put out a press release saying they had taken the decision independently. It is pretty clear."

The Whitehall officials who were invited to view the film on September 24 1965 before it was due to be broadcast included Trend, the head of the Home Office Sir Charles Cunningham, and senior representatives from the British Armed Forces, the Ministry of Defence and the Post Office, which at that time was responsible for granting the BBC its licence to broadcast.

Cook said an internal memo was then put together by the officials for ministers and civil servants about the reaction to the film, which was labelled top secret and sent to Prime Minister Harold Wilson.

But he added: "Wilson is astute enough to realise that he cannot be seen to be explicitly censoring a film because the BBC publicly is an independent body.

"So he writes to his cabinet secretary advising that the government doesn't want to be involved in this - but adds you may wish to communicate your views along with the other civil servants privately to Brook, the BBC chair.

"And that is essentially what happens - ministers don't want publicly to get involved, but they give civil servants the nod that they should communicate their views that the film was unbalanced."

The War Game was not screened by the BBC until twenty years later, in July 1985. The film's director Watkins left Britain to work abroad in protest following the ban.

Cook added: "Essentially the BBC's charter of independence was violated in 1965 ... The key thing is the censorship was entirely consensual."

Among those interviewed for the BBC Radio 4 programme is Sir Christopher Bland, who was BBC chairman of governors between 1996 to 2001.

He said he was "astonished" that the BBC would have agreed to show a film to politicians before transmission.

A BBC spokesman said: "Fifty years on it's difficult for us to comment on the background to the broadcast of this programme."