The author claims women earn less through choice, putting family above work, and not because male bosses are paying them less.

The study flies in the face of recent cases in which City women have sued their employers claiming they are paid less to do the same job or humiliated into such roles as playing the “stewardess” serving drinks on the corporate jet.

The author — a male academic — claims women are motivated most by a biological need to have babies while men are spurred on to increase their earning power to attract a wife.

Women often do not want to return to the “rat race” after having children and so choose to come back to less demanding, less well-paid jobs.

“Even if discrimination magically disappeared, women would still earn less because they do not want to make money as much as men do,” said Satoshi Kanazawa, lecturer in management at the London School of Economics and author of the report.

It may explain why the contestants so far fired by Sir Alan Sugar in his BBC2 show The Apprentice, a quest to find a £100,000-a-year manager for one of his companies, have all been women.

But among those who have a strong motivation to make money — generally those who are under 40, unmarried and childless — the difference in earnings with men disappears.

The report is based on questioning more than 18,000 men and women on their attitudes to work over a 25-year period.

“The analysis of the survey data demonstrates that men are more motivated to earn than women, but this is only because women in general have better things to do, reproductively speaking,” writes Kanazawa in the latest issue of the Journal of Economic Psychology.

According to the most recent government figures, the average pay gap between men and women is currently 18.4%, down from 19.4% in 2003. The official explanation is that women are the victims of male discrimination in the workplace.

Kanazawa argues that men and women have different priorities in choosing jobs. Males are more likely to take work that allows them to earn more. Women choose jobs that allow them to help others, regardless of how lucrative they are.

Women who took part in the survey put greater emphasis on work itself being important rather than the level of income.

High-flying women this weekend said they agreed with Kanazawa’s findings. Sahar Hashemi, 36, a former City lawyer who co-founded the Coffee Republic chain with her brother, and now a speaker on entrepreneurship, said: “Inequality is so over, so not this generation. I find it an insult the way some women go on. It is as if they have a chip on their shoulder.”

Stella David, 42, was last week presented with a lifetime achievement award after the company where she was managing director, Bacardi-Martini UK, finished in the top 10 of The Sunday Times 100 Best Companies to Work For an unprecedented five years in a row. “I have never been pressurised by discrimination. It may exist but the old-fashioned mindsets will disappear over time,” she said.

David, who has been promoted to president of the drinks company’s Asia-Pacific market, added: “Women who leave to have families might want a choice to come back in a less frontline role. If we can organise it, we will.”

Alex Haslam, professor of social and organisational psychology at Exeter University, who last year suggested women sometimes faced a “glass cliff” when they were promoted in failing companies, said: “The basic pattern of this study is correct. Men and women have different career trajectories.”

Kanazawa’s study is published ahead of an interim report this week by the government’s Women and Work commission. It will call on employers to appoint “equality representatives” to monitor salaries. A Department of Trade and Industry spokeswoman said: “With women’s pay almost 20% behind men’s — and double that for part-time work — it is a fact that discrimination exists. Women are demanding a better deal and the government is making sure they get it.”

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