"More women in the country go insane than in any other class in the community," noted Edwin Pratt in a 1904 study of agriculture. He recommended an organisation just starting in Canada: the Women's Institute. Female lives are made of "little things" and, if cooking a meal, washing clothes and keeping chickens can be made a matter of pride, then the home and nation will prosper. Female togetherness and home-making were the aims of the WI. They provoked scorn in my postwar mother, who cared little for keeping chickens or making jam in the sophisticated 1950s and did not believe women should join together. When feminism came along in the early 1970s, the WI seemed an irrelevance to me with its stoking of home fires, its singing of a misunderstood "Jerusalem".

This book supports the view that the WI is "the most important body formed during the 20th century"; feminist with a "down to earth brand about self-respect and just reward", it "helped mould modern Britain" by teaching the arts of democracy. Jane Robinson makes much of the 2000 Annual Meeting slow hand-clapping Tony Blair when he came to speak in a hot Wembley conference centre. It's a good story: an urbane premier deprived of his Autocue facing 10,000 women and relentlessly sticking to a political speech no one wanted to hear. Was this the turning point in his fortunes? Perhaps. The year before, 11 middle-aged Yorkshire women, 10 from the WI, posed naked behind strategically placed cherry buns and the like to make a calendar to raise money for leukaemia research  a feat celebrated in the film Calendar Girls (pictured). Clearly WI ladies were not always ladylike. Yet, apart from these remarkable events, most of the unladylike activity mentioned here was carried out by women outside the movement: the suffragette Edith Rigby hurling black puddings, then bombs (both home-made) when the young Churchill came to speak in Liverpool. The WI itself was concerned less with politics than with cleaner, tidier and more sanitary homes.

Originating in Canada in 1897 with the homely Adelaide Hoodless, the Women's Institute came to the UK in 1915. It did not immediately conquer the shires: indeed one vicar operated a curfew forbidding female parishioners to go out after dark; another man thought that enlightening women was like attempting "to improve the condition of the beasts of the field": a woman taught her power might no longer be "so profuse of her treasures to a hapless infant". WI husbands called the institute "the curse of a married man's life" since a wife outside the home would not have supper ready on time. Other gentlemen, including the energetic and admirable John Nugent Harris, were far more encouraging.

The aims of the WI were democratic, yet its history reveals the British fascination for titles. Coming disproportionately from the upper orders, the leaders gave the movement respectability. The first British WI, formed in Llanfair PG, was patronised by the Marquis and Marchioness of Anglesey: "tea, bread, and one kind of cake" were served as refreshment at meetings. The redoubtable philanthropists included the sporty, unstuffy Lady Denman, the very type of the eccentric Lady Bountiful. Wearing breeches and smoking incessantly, she roared round the country using a wooden football rattle to attract attention to her motorcar. In the first world war her nicotine addiction formed the basis of a charity providing millions of cigarettes to military hospitals. (It's difficult not to feel sympathy for her asthmatic husband.) Mixing the absurd and admirable, Lady Denman played hockey in the ballroom of Government House when her husband was governor-general of Australia, but also worked tirelessly to form a healthcare system for the outback. Most usefully, as longtime head of the WI, she insisted that the institute, numbering hundreds of thousands of members by the 1920s, never come under direct government control.

The WI was associated with wholesome activities: temperance, family planning for the married, mobile libraries, chicken-keeping, and above all jam-making. As so often with women's political development, war had a major impact. After the end of the first world war, the WI campaigned for more education about sexually transmitted diseases as infected solders returned to pure wives. And in both wars jam-making became not just a home activity but a patriotic duty: in one season of the second world war more than 1,500 jars were made by five Kent women. When meat was scarce, rabbit clubs were started to produce food and fur: "Convert British Bunnies into Bombs". Less welcome activity was hosting the town evacuees, especially when marked by "disease or dishonesty" and bringing filthy, lousy children. No wonder WI members embraced adult education after the war.

As a daughter of the WI, Jane Robinson is an admirable enthusiast for her subject, and her book is  perhaps inevitably  tinged with nostalgia for an earlier age, despite the WI's recent support for a YouTube video (on masturbation). It is pleasant to read of people doing good works and enjoying themselves, even if their self-satisfaction may grate a little. I remain unconvinced of the movement as a levelling force, a training for modern civic life in all its tangled complexity. But in the austere future we all face, preparation for a flawed democracy may be less needed than home-survival skills  jam-making and breeding those rabbits.

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.