A DOCUMENTARY which was never broadcast, because the Thatcher government leaned on the BBC to prevent its damaging allegations being made public, is being offered for sale over the internet.

The Secret Society series caused a political furore in 1987. Alisdair Milne was sacked as director-general of the BBC, prompting accusations that the governors were acting under pressure from the government.

Strathclyde Police raided the corporation's Scottish headquarters in Glasgow the next day, seizing tapes of the ''banned'' programme.

The episode argues that successive prime ministers - specifically, James Callaghan and Margaret Thatcher - extended a tradition of secret cabinet committees to make major decisions.

It also details an alleged dirty tricks campaign led by Michael Heseltine, then defence secretary, to discredit CND.

The six-part series included an episode revealing how the cost of the (pounds) 400m Zircon spy satellite had been concealed from parliament.

That episode and four others were eventually broadcast after police returned the tapes but the BBC decided that the episode about secret cabinet committees was too sensitive to show before the 1987 general election.

Duncan Campbell, the journalist who made the series and who now runs a production company in Edinburgh, said that freedom of the press should prevail over any breach of his or the BBC's rights.

''I'm delighted there is still an interest in the video,'' he said.

''In the context of renewed and serious concern about the conduct of governments, it is entirely appropriate to look at the way in which a previous government bullied, harassed and tried to inflict its spin on the BBC. I hope the BBC will remain robust against those pernicious pressures.''

The production team behind the series was threatened with prosecution under the Official Secrets Act. Mr Campbell's front door was kicked down and his home searched.

Pat Chalmers, then controller of BBC Scotland, was also questioned by Special Branch officers for eight hours.

''There was no reason why that programme should not have gone out,'' he said yesterday. ''No-one ever queried the content of that programme.''

Mr Chalmers added that the affair - particularly the removal of Mr Milne and the later arrival of John Birt - damaged the editorial integrity of the BBC.

Channel 4 and Mr Campbell later attempted to buy the ''banned'' episode from the BBC but were rebuffed.

Eventually, the original scripts were used to produce a new version and it was broadcast in 1991 on Channel 4 as part of a season of banned films. However, the original has never been broadcast.

Tony Gosling, a journalist and freedom of information campaigner, who is selling the video through his website, described the significance of the sixth programme.

He said: ''It's about secret cabinet committees - that is ones that even some members of the cabinet are not even allowed to know who's on them - where big decisions, not even discussed in cabinet, are made. You end up with massive decisions, such as whether to buy the Trident submarines, being made by anonymous people.''

A BBC Scotland spokesman said: ''If an untransmitted programme remains the copyright of the BBC and it is being used without our authorisation, then that is something we would ask our lawyers to look into.''