Dr Mapstone is a psychologist. She wanted to prove once and for all that, these days, women and men argue as equals. There was just one hitch: they don't. Hester Lacey reports
I disapprove of what you say, but I will defend to the death your right to say it." Good old Voltaire, sticking up for the universal right to hold one's own opinion. Though he could probably have added: "But if you are a woman, I will have already dismissed whatever your point is before you have even made it, and I will probably snicker dismissively about you afterwards, behind your back." Because in the 18th century, women were expected to be nice and shut up and not argue. What a long way we've come. Or not.

Last week, Dr Elizabeth Mapstone, a consultant psychologist and founding editor of the Psychologist magazine, published the results of a 10-year investigation into the social construction of argument in the British Journal of Social Psychology. The results do not make heartening reading. Dr Mapstone set out to explode the ancient stereotype that a man does not care to lose an argument with a woman; instead, her research resoundingly reinforces the old ideas.

Women, it seems, still cannot easily win an argument against men - because even if they are in the right, simply by defending their point of view they betray social expectations of "feminine" behaviour and damn themselves as strident and hysterical. Women are still expected to be calm, nurturing, placating.

At the same time, while men see themselves as reasonable and rational, they still think women have cotton wool between their ears. Men "assume that women are unable to follow logic or be objective, and so may dismiss their expressions of opinion as unreasonable, irrational and illogical," says Dr Mapstone.

She was surprised and alarmed at the results of her research, which is based on diaries kept by 600 volunteers of confrontations in both their work and home lives. "Originally, my aim in using gender in the experiment was to show it made no difference," she explains. "You can get sick to death of people talking about absurd sex differences - so when I found just such differences I was shocked. There are clear patterns in the material, and the only way to make sense of them is that men are resisting women's demands to be treated as equal. It was very rare to find a man's report of an argument that didn't evoke the stereotype of the irrational, hysterical female. I should say that this does not apply to all men, there are honourable exceptions - but not many," she added ominously.

After each argument, Dr Mapstone asked her volunteers, who came from all walks of life and ranged in age between 20 and 70, to rate their anger levels and how important they felt the encounter had been. Among the patterns she found that men in the workplace usually registered a high level of anger over an encounter with a subordinate woman. "Anger levels would hit the top button, as though they were thinking 'it's not her place to disagree' - so secretaries are constantly on the receiving end of these surges of anger," she says. "With a woman of equal status, men will tell themselves the argument simply wasn't important. And if a woman is the boss, the key feeling is resentment. One's blood runs cold if one is a woman. It is a very dreary picture at work."

But surely progress towards equality in the workplace, though slow, is sure? "I submitted an outline for a book on this subject to a feminist publishing house, and they claimed it wasn't a problem for younger women," says Dr Mapstone. "They asked me to aim it specifically at older women. But all the younger women I meet say 'You were right!' I think 30 is the magic age - a kind of watershed after which you begin to be seen as a threat. At 20 you think you know how to deal with men, but at that age you are still seen as a sexual object - arguing with young women is sexual provocation, and not to be taken seriously." So what's the solution? "I'm not sure what we do about it. It's depressing as hell," says Dr Mapstone.

Can it be true? Surely by now there is a new generation - or several generations - of young women in the workplace who have grown up with the idea of equality and can stand their ground in an argument, without crying, screaming, or stamping their feet? Or is the field not as level as we would like to think?

"I do disagree with men, and I come out ahead," says Alison, 32, in middle management. "It's because I say what I think, and if I know I'm right, I will stick to my guns. They hate me for it. Even my female friends have suggested that I could try to be more feminine in the way I go about things, but I hate that woman-thing that everyone has to like you. This isn't just at work. I remember when I was a student, I was winning an argument in a seminar and the lecturer made me hold up my hand. 'See, her fourth finger is longer than her index finger - a male characteristic,' he said."

"Men try to talk over you," says Caroline, 26, a city solicitor. "In a group meeting, you have to repeat yourself over and over. It's not down to logical skills - you have to stick to your point and not be beaten down, and not let them over-ride you. When I'm trying to be authoritative, I drop the pitch of my voice, because they just don't seem to tune in to a higher voice. Men think there's no problem," she adds. "They think the battle is over for women, and that women have won - you don't really talk about it if you want to keep your job."

"You have to really be prepared to use your verbal elbows," says Anna, 28, who works in university administration. "Once a man just wandered off when I was trying to sort something out with him - just got bored, and decided he wasn't interested. I tend to back everything up with memos, and I am very careful now to keep very calm, speak slowly - never enter a verbal free-for-all even if all six men in the office are plunging in together, because I know I won't even be heard. Rather than trying to shout above the din, it seems to be more effective to speak more quietly - if people have to strain to hear you, they shut up a bit themselves."

As Dr Mapstone observes in her paper, the division starts very early. Sarah, 27, is a teacher in a south London secondary school, with pupils aged 11-15. "The boys are really aggressive and don't hesitate to answer back," she says. "It's accepted that boys will stand up, shout, grab attention, throw themselves round the room, while girls are in big trouble if they do that. The boys are massive, as they get older they tower over you, they are loud, they are almost sexually aggressive - they will say anything to you. If I tell a girl off and she doesn't want to deal with it, she'll walk out of the room. A boy will come right up against you, confront you, be aggressive."

Part of the problem, suggests Dr Robert Edelmann, reader in clinical psychology at the University of Surrey, and author of Interpersonal Conflicts at Work (BPS pounds 8.99), is that any display of assertiveness is still seen as "out of character" for women. "Gender comes before person," he explains. "People don't think 'it's the boss', they think 'it's the female boss'. Women are in a double bind - it's well-documented that men do assume a position of power from their gender, and women find it difficult to assert themselves. We think attitudes have shifted, but it's surprising how little they have done so. There are many subtle ways to use gender-related put- downs."

But is it possible that some contain a grain of truth? "I have always been a women's networker, backing women, encouraging women, out there for women," says Christina Gorna, barrister, writer and broadcaster. "But, though I hate to say it, and you won't like me for it, I have found women in the workplace so damn difficult. On an average basis, women let themselves down over and over again. Some are unable to argue logically, are hysterical, tend to emotional blackmail - you would have thought barristers, of all people, would have learned how to conduct themselves! It is much easier to put a case against a man - there is no comparison. Men are just more logical. They don't like a good argument being put against them by a woman, but they have to accept it. Women have been taught to say yes, and to agree to things they shouldn't agree to, many of them have low self-esteem, but most skills can be learned. It's incumbent on women to be in a receptive frame of mind. We have to teach women how to be equal."

Staggering home from the office war-zone, women may seek a crumb of comfort in brooking no fuss over whose turn it is to take the rubbish out or mow the lawn. As women grow older, they become more confident, and are much more willing to take part in family arguments at home. And they may even enjoy them, up to a point. "At the moment, we're in a no-win situation generally, but one thing I found encouraging is that married couples who liked each other had found ways of resolving arguments pleasantly at home," says Dr Mapstone. "When people live together, they eventually stop seeing each other in terms of gender and start to see each other as people."

CHERIE BOOTH QC: Has attacked the legal profession for sexism. 'Particularly good at spotting the weaknesses in political arguments,' say admirers.

GARETH PIERCE, lawyer: Represented the Guildford Four, the Birmingham Six, and battered wife Sara Thornton. Persistent, no matter how strong the opposition.

BETTY BOOTHROYD, speaker of the House of Commons: Tough, but humorous. "By all means let us have robust argument, but good temper costs nothing."

MARGARET THATCHER, former prime minister: Of her ministers, Heseltine and Lawson were said to be the only ones who could stand up to her.