With their long hair, loose ties and flared trousers, the Pupil Power radicals wanted to overthrow the oppression of the cane and the conformity of school uniforms.

Special Branch and the Government saw them as pawns in a communist plot to undermine the nation between double maths and PE.

Confidential police and Whitehall papers released under the Freedom of Information Act show the official concern at the rise of subversive pupil groups in the late 1960s and early 1970s. Thousands of boys and girls were recruited to the movement, leading to classroom strikes and violent protests. The Schools’ Action Union and the National Union of School Students appeared to threaten the British way of life, demanding an end to corporal punishment, the introduction of free dinners and, for the over-16s, contraception.

Having seen left-wing students bring down the French Government, the Prime Minister, Edward Heath, was taking no risks and ordered MI5 to monitor the revolutionaries, who included boys from Eton and Harrow,

Documents released by the Home Office show that Mr Heath also asked the Education Secretary, Margaret Thatcher, to report. An official replying on her behalf warned there was “significant, but rather ill-defined and inarticulate, discontent” among children. “Some boys and girls are already beginning to develop political attitudes in an immature way, and are affected by the example of militancy set by older students and by adults, including their own teachers,” he added.

Investigations by Scotland Yard’s Special Branch, then at the height of its battle with the IRA, revealed that the National Union of School Students’ campaign was backed by the Young Communist League, the Trotskyist Young Socialists and the Young Liberals. Officials were shaken enough to consider restricting entrance to sixth forms.

In May 1972 the Government and Scotland Yard were braced for a protest by 10,000 pupils planning to play truant to march through London. As the authorities struggled to uncover the radicals’ plans, David Lane, a Conservative MP, forwarded a report based on the accounts of a group of girl “spies” who infiltrated a meeting. “The leaders spoke with Cockney accents and spoke illogically,” said the report. “It seemed there were a number of middle-class kids who were dressing badly to look working-class.”

The march was the high water mark for the classroom revolutionaries.

A Special Branch report estimated that the event attracted only 1,500 pupils. It started in confusion with different groups gathering on opposite sides of the Thames before they joined to march past County Hall on the South Bank with protesters chanting “Uniforms out” and “Caning out”.

Later the pupils split, with half marching to Hyde Park for a brief demonstration while others remained on the South Bank, where they were involved in scuffles with police while chanting: “Attack the pigs.”

A Scotland Yard report revealed that the protesters had planned to hand a letter of protest to County Hall, home to the Inner London Education Authority, but “subsequently discovered the letter had been lost”.

Despite the chaos, Sir Philip Allen, Permanent Secretary at the Home Office, said that it should not detract from its significance “as a symptom of subversive influence”.

The influence of classroom radicals appears to have waned as the oil crisis and miners’ militancy replaced the threat from the school revolutionaries.

Forty years on Pupil Power has achieved most of its aims even if the movement’s leaders appear to have had little impact on modern politics.

Caning was outlawed in state schools in 1987, free contraceptives are now available to all youngsters, uniforms are not worn in many schools and last year the Government announced a trial scheme for free meals for all primary pupils.

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