MARGARET THATCHER’S government plotted to take down an elected trade union leader because he was an “avowed Militant supporter,” Cabinet Office papers have revealed.

The documents show that Downing Street planned to block John Macreadie, who was elected general secretary of the Civil and Public Service Association in 1986, from negotiations on grounds that “subversives cannot be tolerated in such jobs.”

Mr Macreadie, who led the successful 1977 Civil Aviation Authority strike, caused a major upset when he defied the odds to win the union’s leadership election. He was active in the Trotskyist Militant tendency and later joined its successor Socialist Party.

His victory was overturned after a court challenge before he took office, losing the subsequent rerun to John Ellis, a “moderate” candidate.

But in the intervening period, the government considered deploying an “established procedure” which would block any union official who “is, or has recently been, a member of a communist or fascist organisation, or of a subversive group … whose aims are to undermine or overthrow parliamentary democracy … by political, industrial or violent means.” This was necessary because “subversives … cannot be tolerated in such jobs,” one memo said.

The Star discovered the details of the plot in previously secret papers that have recently been released to the national archives.

Mr Macreadie, who died in 2010, went on to be elected the union’s deputy general secretary. He later served as an adviser to Mark Serwotka, the current leader of the CPSA’s successor union PCS.

Mr Serwotka said: “John was a great trade unionist and a friend and, while not at all surprising, it is still shocking to see evidence of Thatcher’s government conspiring against him as part of its wider project to undermine democratic trade unions and reshape society.

“It is tempting to think this kind of extreme reaction is in the past, but the parallels with today are obvious, with this Tory government seeking to complete Thatcher’s work.”

The Cabinet Office said it did not comment on the activities of previous governments, but claimed there was no longer any procedure in place to deny negotiating rights to communists.