Margaret Thatcher took greater interest in the intelligence community than any Prime Minister since Winston Churchill. Her Home Secretary, Willie Whitelaw, told the DG, Sir Howard Smith, that he wished to be sufficiently well briefed to be able to counter “some of the rather extreme advice” Mrs Thatcher had received.

The Service’s briefing was relatively reassuring. The rise in Trotskyism during the 1970s, it reported, was more than counterbalanced by the decline in Communist Party membership: “Taking the position as a whole, though the threat from subversion is serious and in some ways more evident, it is not greater than ten years ago.”

Mrs Thatcher was not convinced. The Winter of Discontent had strengthened the Prime Minister’s belief in the importance of counter-subversion in dealing with industrial disruption. Whitelaw, though more sympathetic to the Security Service view, also believed that secondary picketing and other militant activism during the strike wave “showed marks of skilled and highly co-ordinated direction”.

Mrs Thatcher demanded prompt action to deal with the “wreckers” in British industry, and summoned a meeting chaired by the Cabinet Secretary, Sir John Hunt, to come up with “solutions”. The Prime Minister, Hunt told the meeting, wanted all the “wreckers” to be identified — which would breach the Security Service charter of 1952, limiting its role to “the Defence of the Realm as a whole, from external and internal dangers arising from attempts of espionage and sabotage, or from actions ... which may be judged to be subversive of the State”. Non-subversive industrial “wreckers” were not covered.

Hunt suggested that the 27-year-old directive, written at a time when subversion “loomed less large in the country’s problems”, might now benefit from revision. Smith’s argument in favour of the existing definition of subversion and against attempting to extend it to include all industrial disruption, however, carried the day. The meeting also failed to come up with the straightforward solutions for dealing with the “wreckers” which Mrs Thatcher wanted. The DG argued that ending industrial strife was far more an issue for government policy than for action by the Security Service.

Early in October 1979 Smith learned that Mrs Thatcher had summoned a meeting at Chequers later in the month to “consider action to counter hostile forces working for industrial unrest”. The DG was not invited. The Chequers meeting decided to set up a small unit in the Cabinet Office to use information from both open and secret sources to try to forestall industrial disruption. The Thatcher government’s fears reached a climax during the year-longminers’ strike of 1984-5, the longest in British history. MI5 was less alarmed than the Prime Minister, reporting on April 4 that “subversive organisations were not making a significant impact on events”. Though the Service continued to monitor contacts between the Communist Party of Great Britain and the miners’ leader, Arthur Scargill, Director F believed that the party was seeking — unsuccessfully — to exert “a moderating influence” on him, rather than to inflame the dispute further.

Scargill had been the subject of a Home Office Warrant (HOW), continued by successive home secretaries since November 1973, on the grounds of his contacts with the CPGB. The former MI5 officer Cathy Massiter later recalled that Scargill “would occasionally shout abuse into the phone at the people who were tapping him”. The NUM’s Communist vice president Mick McGahey had been subject to an HOW for most of the period since 1970. According to Massiter: “The tapping of his home telephone ... gave rise to an office joke about the girls who had to listen to Mrs McGahey’s interminable telephone conversations with friends and relatives. But we were able to get information from her chatting about his movements, which he himself was careful to conceal.”

It has been claimed that during the miners’ strike that“every single NUM branch and lodge secretary had his phone monitored along with the entire national and area union leaderships”. These claims are fanciful. Most phone tapping, authorised in every case by HOWs, was limited to leading Communist and Trotskyist militants and those judged to have close links with them. Stella Rimington, then F2, later recalled “agonising” over the justification for continuing the HOW on Scargill, before categorising him as “an unaffiliated subversive” on the grounds that after calling a strike without a ballot,his declared aim was to overthrow the democratically elected Thatcher government.

The Service’s regular (often daily) Box 500 situation reports on the miners’ strike were originally sent only to senior Whitehall officials. In late June 1984, however, Mrs Thatcher discovered their existence and it was agreed that henceforth copies of all the reports should be sent to her through the cabinet secretary. She seems to have read them attentively, complaining on one occasion that at Box 500 report of September 4 that Scargill was planning a statement blaming the National Coal Board for withdrawing from proposed talks had arrived too late for the government to be able to counter it immediately.

A best-selling history of the miners’ strike later claimed that Rimington was heavily involved in orchestrating dirty tricks against the NUM. According to a Commons motion by a group of Labour MPs, Roger Windsor, the NUM executive officer during the strike, was “an agent of MI5 under Mrs Rimington, sent into the NUM to destabilise and sabotage the union at its most crucial juncture”. Since Security Service policy is neither to confirm nor to deny the identity of any alleged agent, it is impossible to comment on these allegations. However, it is clear that Rimington, like the Service leadership, was determined that the Service’s role during the strike should not go beyond the terms of its charter.

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