BRITISH politics, it is widely noted, now revolves around two axes: left v right and open v closed. But a third one predates both. In the English civil war the Roundheads (parliamentarian and prim) defeated the Cavaliers (royalist and flamboyant), then lost the peace. The taxonomy lives on not as ideology but as two demeanours. Westminster’s Roundheads are sober, earnest and severe: think Margaret Thatcher, Gordon Brown and Theresa May. Its Cavaliers tend to be swaggering, arch and clubbable: David Cameron, Nigel Farage and to a lesser extent Tony Blair. The Cavaliers tend to have the most fun and get the best press. It is no coincidence that the supreme Cavalier of Britain’s recent political past was also its supreme diarist: Alan Clark. “I only can properly enjoy carol services if I am having an illicit affair with someone in the congregation,” he once wrote.

Harriet Harman, Labour’s former deputy leader, is as roundly Roundhead as Mr Clark was confidently Cavalier. Her new autobiography, “A Woman’s Work”, is as serious as his books are riotous. Reading it, Bagehot was reminded of Oscar Wilde’s maxim that “the trouble with socialism is that it takes too many evenings”. The same, it seems, is true of the feminism to which Ms Harman has dedicated her career—first as an activist lawyer, then as a backbench MP, later as a minister. Over 400 pages she documents four decades of brow-furrowing evenings: procedural meetings, resolutions, commissions. Her very language bears the dusty whiff of the committee room: “Taking the fight to the Tories is undoubtedly an important role for Labour in opposition”; “Frank was…not respected by the welfare stakeholders”. “Ever ready to solve rather than cause problems, I…” begins one sentence, without irony (using humour would “deepen the problem of me not being taken seriously”). This is a book on a mission: to counterbalance what the author calls the “vanity projects” written by her male colleagues. It is not one for the beach.

Yet it is one to read. For it makes a fine case for the Roundhead tendency in politics. It charts how the achingly slow, often thankless and arduous work of modernising society routinely meets resistance where it should not: getting wages and health care recognised as women’s issues, introducing measures to raise the proportion of women MPs, improving child care, increasing the pitifully low rate of prosecutions of domestic-violence perpetrators. And at every step of the way, vast walls of opposition. When Ms Harman opposed all-male shortlists, she was informed that working-class women were not interested in politics. When she was made social-security secretary, her deputy told civil servants to bypass her and take big decisions to him. When she beat a mostly male field to become Labour’s deputy leader she was not, unlike her male predecessor, made deputy prime minister. To the tabloids and the sort of Neanderthal MP who sees her as a menace she is “Harriet Harperson”, “Harridan Harman”, “bossy”, “icy” and “shrill”.

The best illustration of what hard, unglamorous and unpopular work it can be to advance changes that ought to come naturally is Ms Harman’s account of how Westminster has evolved, and how it has not, since she first won her south London seat in 1982. Back then 97% of MPs were men; women were even outnumbered by MPs called John. She describes the dismal experience of late-night votes, when MPs waiting to speak would get progressively more drunk, then would give progressively longer speeches, then in the early hours would subject her rounding-up speech to “inebriated jeers”. The book contains some jaw-dropping anecdotes. In 1983 an anonymous MP complained that Ms Harman had voted with a baby under her coat; she was embarrassed to tell the clerks it was just the residual weight from a recent pregnancy. When she argued for more family-friendly hours in Parliament she was accused of being a marriage breaker: apparently MPs’ wives would not trust them “being out and about in London in the evenings”. Desperately slowly, one tiny step at a time, Ms Harman and her comrades chipped away at this culture. Today, thanks to their efforts, there are 195 women MPs, Parliament’s hours have been reformed and there is a crèche for children of MPs and other staff.

Yet depressingly much stays the same. Ms Harman’s description of the press lobby and the legislature when she arrived—“a boys’ club being reported on by a boys’ club”—still holds. The House of Commons is more male (70%) than equivalent legislatures in Algeria, Belarus and Sudan. Recent studies of correspondents in Westminster put the proportion of women at around a quarter. The boozy, late-night, wood-panelled stuffiness of the place lives on, as recent news stories have shown. A survey of 73 women MPs by the BBC last month found that almost two-thirds had experienced sexist comments within Parliament (a male MP told one she should be “in the kitchen washing dishes”). In a debate on January 30th a troglodyte Tory woofed at a woman MP as she spoke. In a text-message exchange leaked to the newspapers last weekend David Davis, the Brexit secretary, denied having tried to kiss Diane Abbott, the shadow home secretary, in a Westminster bar: “I’m not blind,” he chortled.

Thank you, Harriet Harperson

The sheer inertia slowing changes to all this, so easily underestimated by commentators, is why politics needs Roundheads. With their compromising bonhomie Cavaliers are useful consolidators, lubricators of relations between social groups, guardians of good humour and thus perspective. But leave politics to such types and it becomes a golf club bar. For it to work, they must be joined by the likes of Ms Harman: Roundheads willing to tread a stonier path. These politicians make enemies, call out bad consensuses and gradually, painfully reform the common sense of the age. “Today’s heresy is tomorrow’s orthodoxy,” she writes in “A Woman’s Work”. How well her story illustrates this truth.