A time warp of 1970s sexist attitudes is driving women in their late thirties from careers in science and technology and undermining key sectors of the economy, according to an international study.

Researchers claim to have discovered a “hidden brain drain” as women opt out when facing a choice between family life and pushing for promotion at work.

The majority choose their children and alternative careers instead of struggling with the hurdles of a macho “lab coat culture” with long hours, old boys’ networks and the risk of sexual harassment.

Sylvia Ann Hewlett, an economist at the Center for Work-Life Policy in New York and the lead author of the study, said the research had revealed a world with values seemingly stuck in the 1970s.

She said: “It has been a bit like a time warp. This predatory or condescending culture [towards women] was more common across the workplace 20 to 30 years ago but has somehow survived in an engineering, science and technology context.

“It is the hidden brain drain. We have this amazing, talented pool of women who have left the industry. It is highly destructive to our society and economy.”

In Britain more than 225,000 science, engineering and technology (SET) graduates are not working in the industries for which they are qualified, and 50,000 of those are not working at all, according to official statistics.

The report claims the “sexist culture” persists despite concerns about dwindling numbers of female graduates staying the course. The European Commission has predicted that Europe will suffer a shortfall of 20m skilled workers in science and technology by 2030.

Hewlett and her colleagues followed the careers of 1,000 women with SET qualifications in companies in America, and surveyed 3,000 staff employed internationally by three multinational companies. They also sought the opinions of women in cities including London, Palo Alto, New York and Shanghai in 28 focus groups.

The study, to be published in the Harvard Business Review on Thursday, found that while women made up 41% of newly qualified technical staff, more than half dropped out by the time they reached their late thirties.

Nearly two-thirds of all women surveyed said they had been victims of sexual harassment in the workplace. A similar number objected to the “lab coat culture”, in which researchers laboured over experiments, “tethered to the microscope”, for up to 12 hours a day.

Nancy Lane, a cell biologist at Cambridge University, recalled the conflict she felt between work and her two children. “I felt forced to make agonising trade-offs, asking myself, ‘Do you abandon an experiment or abandon a needy child?’ ” she said. “I found myself deliberately choosing questions that allowed me to run experiments in a five-day week.”

A total of 43% of female engineers said they had encountered an inherently sexist culture in which it was assumed that only men had the skills to succeed in the most advanced posts.

The situation was familiar to Elspeth MacFadyen, a programme director at BT’s chief technology office who now specialises in fibre optics. MacFadyen is one of 13,000 BT employees who now work from home full-time but says she can recall the days when women deliberately dressed down to blend in.

“I remember having to wear jeans and a shirt; otherwise people would think you were secretarial. It’s better today but the macho culture still exists,” she said.

Olivia Judson, a science television presenter and author, decided against a full-time career in academia. She said: “One of my PhD supervisors told me that a lot of the women he had supervised ended up leaving science. Men were more likely to be overconfident and women were more likely to be underconfident, even though there was no difference in their abilities.”

Even in space women are not immune. In 1991 Helen Sharman, Britain’s first astronaut, was greeted in the Mir space station by Anatoly Artsebarsky, a Russian cosmonaut, with the comment: “Space . . . is hard work, not a woman’s work.”

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