Thirty years after Margaret Thatcher became prime minister, the position of women in British politics could hardly be more dire. David Cameron, William Hague, George Osborne and Chris Grayling hold the top jobs in the shadow Cabinet. Nick Clegg, Vince Cable, Chris Huhne and Edward Davey lead the Liberal Democrats. Only Labour has a woman in one of the very top jobs – Harriet Harman, who was elected deputy leader of the party two years ago – but even she has been denied the deputy prime ministership enjoyed by her predecessor, John Prescott.

This is a disgrace and a scandal. It should also be a crisis, prompting the country's political leaders to ask themselves hard questions about their prejudices towards women. In that context, Harman's demand that Labour should never revert to a duumvirate seems modest and reasonable. That won't stop some Labour backbenchers muttering among themselves and making the kind of sneaky comments which will no doubt surface in right-wing journals: women wouldn't need special quotas if they were any bloody good, Harman's equal-opportunity agenda will ruin the economy, and so on.

But look at what she actually said in the interview which has caused such a furore: "I think it's a thoroughly bad thing to have a men-only leadership." So do I. What's controversial about that? I'm not suggesting women should rule the world, just that we should have equal access to the top jobs. It's a fair bet that Cameron's first Cabinet won't have a female Chancellor, Foreign or Home Secretary, and Harman herself is an anomaly in a Labour administration which has retreated from the heady days when almost a third of Tony Blair's Cabinet were women. As a rule, the Lib Dems don't matter as much as the two main parties, but they could hold the balance of power after the next general election and the absence of women at senior level exposes the emptiness of their claim to offer a radical alternative.

"In a country where women regard themselves as equal, they are not prepared to see men running the show themselves." That's Harman again, and millions of women – who have votes – agree with her. We don't think there's anything natural or reasonable about the preponderance of men in politics, and we've put up with it only because there hasn't been a choice; it is a well-known fact that parties have always tended to pick male candidates for winnable seats. In the old days – by which I mean as recently as the spring of this year, when for various reasons everything began to unravel – old loyalties were powerful enough to allow political parties to go on behaving as they always had. With an unprecedented number of MPs standing down at the next election, I'm not sure any of the parties can rely on that in future.

Here's a final quote from Harman: "I think a balanced team of men and women makes better decisions." Again, you would have to be an out-and-out misogynist to argue with that. Of course, no one who attacks Harman will admit to that, although they reveal their personal venom in cheap remarks about her name – they love to call her "Harperson" – and her posh background. The right has developed a sophisticated argument about gender difference that doesn't openly denigrate women but has the effect of maintaining the status quo, which is grossly unfair to women.

No one should ever underestimate the incredible power of the status quo. Most people believe that what they grow up with is normal, even if a moment's reflection shows that it's actually unfair and elitist. With notable exceptions, like Lady Thatcher, the political establishment in this country has always been male-dominated; anyone who challenges it can easily be portrayed as shrill and envious. The argument that something has always been done in a certain way has immense appeal, as the front benches of the three main parties show, unless you happen to be one of the people who lose out because of it.

In the case of British politics, it's undeniable that millions of women are not being properly represented and there could not be a better symbol than the fact that we don't even have equal pay. The percentage goes up and down by a few points year by year, but what doesn't change is that women tend to be paid less than men; on this issue, trades unions with their male general secretaries are as culpable as politicians, having consistently failed to make equal pay one of their top priorities. It's been left to firms of solicitors to bring lawsuits against employers, including local authorities and hospitals, which haven't complied with legislation that was supposed to address this unfairness more than three decades ago.

In her interview yesterday, Harman appeared sanguine that Labour wouldn't go back to the days when the leader and deputy leader of the party were both men. She may be trying to achieve though public pressure what she hasn't been able to do in private; her attempt two years ago to change the rules got nowhere because the party's hierarchy threw its collective hands up in horror. That was just after she became deputy leader and since then things have arguably got worse; Lord Mandelson, who isn't even an MP let alone elected by the party, is now Brown's No 2 and de facto deputy prime minister.

In the end, this debate is about being modern. Those of us who live in European democracies support a view of human rights based on equality and fairness, yet our political structures signally fail to reflect it. So do pictures of the present Cabinet and TV coverage of both houses of Parliament.

What kind of image does this country want to present to the world? Brown is scarcely better than Cameron or Clegg on this issue, and all three of them need to think about the message they are sending to women voters – and political leaders in other countries where women have many fewer rights. Our leaders should come clean about whether they believe their own rhetoric on gender equality, and accept that they're in danger of being regarded as hypocrites if they don't put it into action.

Harman is absolutely right to say what she did, and millions of women are quietly cheering her on.