THE collaboration between the three pro-Union parties in the Better Together campaign may seem unprecedented, but files from the 1970s show it also happened then as the SNP's popularity grew and a referendum loomed.

Last month Labour peer Lord Foulkes tried to intervene over the Road to Referendum series on STV, written and presented by Herald columnist Iain Macwhirter, but in 1977 a proposed BBC series looking at how an independent Scotland might look sent the leaders of Labour, the Liberals and the Tories into near apoplexy.

Aside from threats to broadcasters and high-level dealings between the SNP's opponents, there was internal Labour Party rivalry about who should deal with the issue as a turf war erupted between the Scottish Office and other senior Labour figures, in particular future leader John Smith.

In the spring of 1977 the Labour Government of James Callaghan and his Scottish Secretary Bruce Millan heard word that BBC Scotland was planning a television series based on the book Scotland 1980 which sought to envisage what an independent Scotland might look like.

Scottish Office Minister Harry Ewing, shown in these internal papers as far more combative behind the scenes than in his public image, hit the roof.

"I have made certain enquiries which in my view reveal a very serious situation – serious enough indeed to warrant intervention by the Government at the most senior level," he wrote.

"The timing is absolutely devastating in that [the series] will be screened just prior to the district council elections in Scotland. There can be absolutely no doubt that their effect on the outcome of the district council elections will be to say the least disastrous, not only for the Labour Party but for other political parties in Scotland as well."

Mr Ewing stressed: "My strong conviction is that the programme will be heavily weighted against the Government and against those of us who are not in favour of separation."

He also added: "It is interesting to see that the matter was first drawn to our attention by Mr Francis Pym and it must be for consideration whether or not the Government should advise Mr Pym, and indeed the Liberal party, of our findings on this matter."

Pym was a Tory whip who had been Edward Heath's Northern Ireland Secretary and would later serve as defence secretary under Margaret Thatcher. Papers show he met cabinet minister Michael Foot to express concern that the "media should be devoting too much time and attention to the possibility of an independent Scotland. This concern is shared by ministers here."

John Smith, as Privy Council minister, was in overdrive, co-opting Helen Liddell as secretary of the Scottish Labour to use her influence as a recent BBC staffer. It was agreed "to recommend that all three parties (Labour, Liberal and Conservative) write independently and simultaneously to the BBC, either at UK level to Sir Michael Swann, or at Scottish level."

Privy Council Office Secretary Bill Price was also to approach Peter Hardiman Scott, the BBC's political editor about the programmes "to see whether the BBC were prepared to take internal action to stop them being screened. If this approach were unsuccessful further action at a higher level might be considered."

Donald McCormack of BBC Scotland's Public Account programme attempted a deft move, inviting John Smith to appear on the final debate programme. This prompted some internal party strife, with Harry Ewing seeking to veto such an appearance on the grounds that "Mr Smith is no more a Scottish Office Minister than any other Scottish MP in a UK department. In my view, the Secretary of State himself should do the first programme, and I am not in favour of any minister taking part in the second."

The programmes were screened, the book was published, newspaper articles appeared. Labour suffered the predicted blow in local elections, and two years later Scots voted in favour of a Scottish Assembly, but not by the 40% threshold imposed.

Angus Robertson, SNP Westminster leader said: "These dusty old documents show that the Westminster parties being in cahoots with each other, and trying to control from London what happens in Scotland, is nothing new.

"It is extraordinary that they ganged up to bully the BBC for overtly political reasons. They were panicking about losing control of Scotland then, which is the same reason they are mounting the disreputable Project Fear operation against a Yes vote now."

Dennis Canavan, then a Labour MP but now a leading figure at pro-independence campaign Yes Scotland, said: "The correspondence shows the paranoia which existed at that time about the possibility of Scottish independence. It also shows the degree of collaboration which existed between the Unionist parties in their desperate attempts to control the media, especially the BBC. Here we are over thirty years later and the correspondence of the 1970s provokes a feeling of deja vu."

Professor James Mitchell of Edinburgh University was not surprised by the controversy and the pressures on broadcasters, given that Britain in 1975 had been declared insolvent by the International Monetary Fund and North Sea resources were vital to bailing the country out.

At the same time the McCrone report highlighting the value of North Sea Oil was hushed up.

Professor Mitchell added: "What is striking in extensively looking through files is the disjuncture in public statements playing down the value of oil and the private acknowledgement that this oil was a godsend."