Deborah Cameron's favourite postcard bears the slogan: "Men are from Earth. Women are from Earth. Deal with it." Having spent 30 years looking for evidence of language differences between men and women, she is flabbergasted that it is now an accepted 'fact' that men and women use language differently.

For those of you who have been on another planet for the past 15 years, I should explain that in 1992, John Gray wrote a best-selling self-help book called Men Are From Mars, Women Are from Venus. His theory was that men were originally hunters and still behave in ways that can be explained by biology. Women are gatherers and destined by biology to act in stereotypically feminine ways - talking and gossiping more and avoiding direct competition. He advises women to allow men to "retreat into their caves" and says it is unfair to expect husbands or partners to try to explain their behaviour.

In the academic circles she frequents, the book was treated as a joke, but Deborah finally decided that his ideas had pervaded popular culture to such an extent that a serious fightback was needed. As she was due a sabbatical, she has released her own popular potential blockbuster, called The Myth of Mars and Venus.

"The book is based on my research, but also on a lot of other people's research. What I am saying is quite orthodox in the academic community," she said.

Prof Cameron is interested not just in debunking the myths, but also in working out why Gray's ideas are so popular. She said: "Some people argue the differences are because of nature; others say it is nurture: but the evidence does not support either view."

She searched far and wide for evidence to support the idea that men and women communicate differently, or that women talk more than men. "I found plenty that was anecdotal, exaggerated or just plain made up," she says, "But nothing that would stand up. People are making huge claims that must not be taken at face value, because the evidence does not say that - it says something else."

She is enraged at the circular nature of the arguments. In her book, she quotes so-called 'evidence' which turns out to come from other self-help books. "We don't expect the same standards from self-help as from science - that is why I'm critical of apparently reputable scientists who take their evidence from self-help books."

Now 49, Deborah grew up in the 1970s and is no stranger to theories that benefit men.

"I wanted to got to university, but my mother died and my father considered it was my job to take her place and look after him. My first job was in an NHS laundry. The women who used ironing machines got £40 a week and the men who were loading washing machines got £60. This was after the Equal Pay Act, but it didn't apply because we were doing different jobs. They were allowed to earn overtime, as well.

"Then I decided to better myself by going to work in the Midland Bank. All the men who had A-levels were sent to do management training. I said 'I've got A-levels', but my boss said: 'They're going to be bank managers and you aren't.' I started going to the library and reading books about feminism."

After eventually leaving home and reading English at Newcastle University, she threw herself into academic life, and in 2004 was appointed to one of the top posts in her field, as Oxford's Rupert Murdoch Professor of Language and Communication. The title was previously held by Jean Aitchison, another myth-buster, who used the Reith Lectures to argue that 'correct' English was constantly changing.

Deborah suspects the 'Mars and Venus' has caught on because it gives people a way of avoiding more substantial problems arising from the huge changes in women's lives over the past 50 years.

"We are an experiment in what happens if you give men and women the same education, the same aspirations and the same career opportunities. We are more similar than the men and women in any other society in history. Economic differences and cultural differences are much more significant for us than gender."

While the idea that men are naturally bad communicators is merely patronising, the danger of the notion that men and women don't understand each other has been illustrated by its use as a defence for rape.

She points out that if communication skills were so important, women would be in charge of all our major institutions. "Like the idea that men are no good at housework, the idea that they are no good at talking gets some men out of something they would rather leave to women."

Writing for a popular audience was a huge challenge for her, but one she enjoyed. "I think if you have ideas that you feel passionate about, it ought to matter how many people you are telling. If you are an academic, the answer is 'not many'."

Her keen eye for bullshit seems likely to find plenty of new targets. She mentions 1970s-style therapy and neurolinguistic programming. "My next step might be communications skills teaching and consultancy, which is also based on myths."

The Myth of Mars and Venus is published by OUP at £10.99.