It wasn't just the unions the Hairies had in their sights

Left-wing groups in the 1970s long suspected they'd been infiltrated, and now they know with the exposure of the 'Hairies'. This is no historical footnote, writes Paul Lashmar. Their secret files wrecked lives and careers

Tariq Ali, the veteran activist, has been huffing and puffing at the news that Special Branch infiltrated left-wing groups he belonged to in the Seventies.

"That's the undemocratic nature of intelligence agencies," he complains. "The state defending itself against its own democratic citizenry. In order to do so it has to disregard some of the democratic values it believes in."

Naturally, one of the undercover police officers involved has a very different take. "It was the best job I ever did in my police service," says "Geoff". "It was salaried schizophrenia but I do think we prevented serious disorder on the streets of London and even stopped innocent people being killed."

Geoff is one of several officers who talk about their undercover work for the first time on BBC2 tonight. Peter Taylor's documentary True Spies reveals the existence of an élite unit nicknamed The Hairies – because officers had to dress the part, grow long hair and take a relaxed view of personal hygiene.

Whatever Ali says, left-wing groups knew all along that they were the targets of infiltration. They were rather proud of it. Jokes about polished size 12 police boots poking out from underneath dirty greatcoats (the de rigueur garb of activists at the time) were common currency.

Special Branch, the closest we have to a political police squad, had informers in the trade union movement long before the 1926 General Strike. True Spies alleges that some 23 senior trade unionists were recruited as unpaid informers during the Sixties, including the moderate union leaders Joe Gormley and Ray Buckton.

But the security services were so obsessed with the threat of Communism they had little insight into a new breed of radicals. In May 1968, French students turned the streets of Paris into a revolutionary war zone. Youths in other countries were inspired to protest against what they saw as the stifling hypocrisy of the previous generation. They challenged capitalism and conservatism wherever they saw it.

A profound disgust at the Vietnam War temporarily cemented the many strands of the left together in powerful alliance. And after the violent clashes in Grosvenor Square, when pictures of police horses being felled by marbles and demonstrators being beaten with batons were flashed across the world, politicians wanted to know why they had not been warned.

The Hairies went into action against an anti-apartheid campaign to disrupt the whites-only South African rugby team tour of Britain in 1970. The campaign was headed by Peter Hain, who was elevated to a cabinet post only last week. A Hairy called Mike became Hain's number two, providing intelligence that enabled the police to prevent the disruption of matches. Hairies also infiltrated the Troops Out movement, the H-Block cam- paigns, the Anti-Nazi League and a wide range of political organisations and Trotskyite groups.

In fairness it is the job of the secret services to monitor groups whose activities might involve violence. If MI5 did not keep an eye on Islamic fundamentalists operating here today we would want to know why. Some Sixties radical groups, such as the Angry Brigade, did turn to violence. The left also flirted dangerously with the IRA.

But far more sinister and worrying than anything revealed in tonight's documentary is the poor quality of much of the "intelligence" gathered in the Seventies and the dubious uses it was put to. We now know it was fed into MI5 files which were to blight the lives and careers of tens of thousands of ordinary people. Often inaccurate or just plain wrong, the files were used in a vast secret operation that smacks of McCarthyism.

One of the most striking examples of this was MI5's secret vetting of BBC staff. Back in 1985 I was one of a team of journalists who revealed the existence of the "Christmas Trees", distinctively shaped green tags discreetly appended to the file of anyone who applied for a BBC job but was identified as a potential subversive. MI5 had been vetting all editorial applicants to the corporation from the late 1930s onwards, but only a handful of BBC personnel staff knew what the trees meant. Unsuccessful applicants were never told why they were turned down; nor could they challenge the accuracy of the information used against them.

Isobel Hilton, now one of Britain's most highly regarded journalists, was interviewed in 1976 for a reporter's job with BBC Scotland. The interview board recommended she get the job. The decision was referred to the personnel office in London, a matter of routine, but then there was an inexplicable delay. We now know Hilton failed her vetting because she had been secretary of the Scottish-China Association. "It is regarded as suspect and so she cannot be appointed," a security officer told a senior BBC manager. The Scottish-China Association was a small cultural group based at Edinburgh University, which was beyond suspicion. It was clear MI5 had confused it with a similar named group believed to be a Communist front. Hilton heard nothing for four months, so she took up a job with the Daily Express.

There were many others. Michael Rosen, now a regular broadcaster on Radio 4 and writer of children's books, was rejected by MI5 for his political background. Steve Hewlett is now a senior figure in commercial television and was editor of Panorama at the time of the interview with Diana, Princess of Wales. In 1982 he was turned down for a job in the BBC because he had been a youthful member of the Communist Party. Secret vetting extended across a wide range of civil service and defence industry jobs. Jack Straw and Harriet Harman were student activists who became the subjects of MI5 files, difficult as it is to imagine them as enemies of the state now. The former civil servant Clive Ponting painted a frightening picture of MI5: "They're utterly reactionary, tucked away in their little world of their own." Miranda Ingram, who had just left MI5, agreed, "Some of them thought that people who wore jeans were potentially subversive."

The underlying problem was that the establishment did not understand the nature of the New Left, which remained the case for more than 20 years after Grosvenor Square. While the Cold War lasted, politicians and intelligence officers saw the world in polarised terms: the Communist Bloc versus the West, evil versus good. You were with us or against us.

Such people could not comprehend radicals who did not want to join either side but wanted what they saw as justice. In 1984, for example, Mrs Thatcher called 140,000 striking miners "the enemy within" even though many of them came from the same families and communities as soldiers who had fought in the Falklands war.

Such comments are now seen as part of a reactionary age; and MI5 now seems more open and democratically accountable than it was even a decade ago. But will we look back in 30 years' time and be astonished at which of today's hairy radicals were grassing on their peers? That is the trouble with spies: you never know.