Jane Robinson's centenary history of the Women's Institute sets out to show that the organisation is not all about jam and Jerusalem. Instead, Robinson's WI is a feminist force to be reckoned with; not "blood-and-thunder" feminism, admittedly, but a "more down-to-earth brand to do with self-respect and just reward".

The problem with this argument is that WI women have always made jam. During the second world war, five "jam-busters" produced 1,500 jars between them in a single season. And they've always sung "Jerusalem" (in a key almost beyond human hearing, said Joyce Grenfell, attending a WI meeting in 1936). They sang it demurely in the early days, patriotically during the second world war (even when, in one village, the Home Guard had chopped the legs off the piano and the pianist had to lie on the floor), and rebelliously in more recent times. A few years ago, a group of WI demonstrators in Gloucestershire roused hundreds of marchers into singing "Jerusalem" at a protest against hospital closures.

Yes, they've had their radical moments along the way. Famously, they slow-clapped Tony Blair off the stage during his speech at their AGM in 2000, one year after a group of courageous middle-aged Yorkshire women had bared all for the calendar celebrated in Calendar Girls (though perhaps they didn't quite "conquer the world", as Robinson suggests). WI women have always campaigned for radical, unladylike issues: in 1922, they were vociferous in demanding better education about sexually transmitted diseases, after huge numbers of soldiers returning from the first world war infected their wives.

The organisation has had its share of impressive leaders. The most redoubtable was Lady Gertrude Denman, who was in charge before and during the second world war. She was the archetypal feisty English eccentric, driving her pony through her country estate using a frying pan for a whip, axing down trees along the way. And she got things done. As the wife of the governor of Australia, she managed to introduce healthcare to the Australian bush when she wasn't busy playing hockey in her ballroom. As the head of the WI, she tirelessly promoted education and social reform.

But even Denman's tone could be saccharine when it came to the WI. "I think that country women are the salt of the earth," she announced in 1946. And although she herself was refreshingly free from class-consciousness, many individual WIs remained inward-looking and parochial under her leadership. In the 1930s, WIs throughout Britain "adopted" families of the unemployed in a spirit as patronising as it was helpful. During the war, several WI branches protested about having to take in refugees from the city, complaining that they would be diseased and dishonest.

Thanks to Robinson's wide-ranging research and stylish writing, A Force to Be Reckoned With is a spirited and engaging read. But it's a book for the already converted. Although not a WI member herself, Robinson is happily seduced by its rhetoric. "The WI made friends of strangers, confident speakers of the shy, and skilled craftswomen of haphazard amateurs," she writes.

Yes, but did that actually make it a force to be reckoned with? "It was hard to be too gloomy if you were enjoying a game of blindfold pin the moustache on Hitler… or sitting with your closest friends in the blackout knitting army socks for other mothers' sons," she remarks with more enthusiasm than irony when describing the wartime activities of the WI.

Ultimately, the WI emerges as an organisation of self-satisfied rural women, doing good and having fun along the way. They remain wholesome even when they're posing nude or pole dancing. The WI clearly still does much to promote friendship in a society preoccupied with ambition, competition and sex. In this sense, it's providing a useful service. Thankfully, however, it's possible to be a dirty, unfriendly town-dweller and still be generous as a friend and fellow citizen.