Ministers are facing demands for an official apology to at least 80 Asian women who were subjected to "virginity tests'' by immigration staff when they tried to come to Britain in the late 1970s.

The demands follow the disclosure of confidential Home Office files that show that intimate examinations – used to "check the marital status" of Indian and Pakistani women coming to Britain to marry – were on a far wider scale than was previously known.

The practice was banned in February 1979 after the Guardian exclusively reported that a 35-year-old Indian woman teacher was examined by a male doctor when she arrived at Heathrow to test whether she was a genuine wife-to-be who had not borne children and was still a virgin.

The Home Office initially denied that any internal examination had taken place. The woman told the Guardian's then social services correspondent, Melanie Phillips, that she only signed a form consenting to a "gynaecological examination, that may be vaginal if necessary" because she was frightened she would otherwise be sent back to India.

"A man doctor came in. I asked to be seen by a lady doctor but they said 'no'," she told Phillips. "He was wearing rubber gloves and took some medicine out of a tube and put it on some cotton and inserted it into me. He said he was deciding whether I was pregnant now or had been pregnant before. I said that he could see that without doing anything to me, but he said there was no need to get shy.

"I have been feeling very bad mentally ever since. I was very embarrassed and upset. I had never had a gynaecological examination before."

The recently released Home Office files report the doctor's version of the examination: "Penetration of about half an inch made it apparent that she had an intact hymen and no other internal examination was made ... The only time she was bare chested was for the X-ray examination… The doctor told the immigration officer verbally that the lady had not had children and she was then given conditional leave to enter for three months as a fiancee." But the file also reveals that after the incident became public the Home Office offered the woman £500 to ensure she did not sue. The payment, offered through her solicitors, was to be "in recognition of the distress she had been caused" but she also had to agree "not to initiate any proceedings against the Home Office".

It was stressed that the payment was not "compensation", which would have implied that immigration staff had acted improperly, and the then home secretary, Merlyn Rees, while expressing his "deep regret" carefully, did not make an official apology to her.

In the face of an immediate storm of protest from the Indian government and elsewhere over such a "humiliating and obscene" practice, the then Labour government confirmed that the incident had taken place but insisted there had only been two other cases in the previous seven years.

But the internal Home Office files dug out of the National Archives in London by two Australian legal academics and seen by the Guardian, show that the practice was far more widespread, especially at British high commission offices in India and Pakistan.

Despite denials by ministers, including in a personal message from James Callaghan to the then Indian prime minister, the papers show that British entry clearance officers in what was then called Bombay, New Delhi and Islamabad all "sought medical opinion on the marital status of some female applicants". In private, senior Foreign Office officials reported 73 cases in New Delhi and a further nine in Bombay over the previous three years.

The Australian academics, Marinella Marmo and Evan Smith of Flinders University law school, Adelaide, said the use of gynaecological examinations on migrant women from the Indian subcontinent in the 1970s was one of the gravest abuses of discretionary powers in British immigration history: "A proper apology that acknowledged 'virginity testing' was not an isolated incident was never issued," they said.

The demand for an apology was backed by the Joint Council for the Welfare of Immigrants, which was involved in the original 1979 case. Hina Majid, the JCWI's legal policy director, said: "This represents yet another shameful chapter in the ignominious history of British immigration control.

"It is deeply regrettable that no apology has ever been rendered to those women who underwent this degrading and discriminatory practice.

"Whilst this is a practice of the past, it is demonstrative of a wider, and indeed ongoing tendency to sideline women in immigration policy making. Whilst in 2011 we may no longer be virginity testing South Asian brides, the sad reality is that many migrant women continue to be denied equal treatment, and the full enjoyment of their human rights," she said.

A UK Border Agency spokesman said: "These practices occurred 30 years ago and were clearly wrong. This government's immigration policies reflect the UK's legal responsibilities and respect immigrants' human rights."