Almost two decades before Margaret Thatcher became liberal Britain's No1 hate figure there was another woman with firm convictions and an even firmer hairdo who inspired almost as much progressive revulsion. For much of the 60s and 70s, and on into the 80s and even 90s, Mary Whitehouse managed to get up the noses of everyone from pornographers to pop singers.

Dramatists poked fun at her, a hardcore magazine and a comedy sketch show were mockingly named after her and Roger Waters denounced her in Pink Floyd's Pigs as a "house proud town mouse all tight lips and cold feet". What was it about this housewife and former art teacher from Wolverhampton that got everyone so worked up? An evangelical Christian and self-styled moral crusader, she set out to stem what she saw as the polluted tide of the permissive society, particularly on television, and most specifically on the BBC.

She wrote her first letter of complaint to the BBC in 1963, the year Philip Larkin said that sex was invented. In 1964 she launched the Clean Up TV campaign and in 1965 the National Viewers' and Listeners' Association  a sort of middle England version of the Saudis' Committee for the Promotion of Virtue and Prevention of Vice. Almost nothing appeared to escape her condemnation. Tom and Jerry, Nationwide, documentaries about the Nazis, Whitehouse complained about them all. Alf Garnett from Till Death Us Do Part and the playwright Dennis Potter were guaranteed to make her reach for her letter writing pad.

Without having seen the play, she was jubilant at the BBC's decision in 1976 not to screen Potter's Brimstone and Treacle. "While it is difficult to pre-judge a programme," she wrote to the director general Alasdair Milne, "I can only assume that Brimstone and Treacle was more offensive than Tuesday night's Dennis Potter play Double Dare. In that case, it must indeed be bad."

Throughout the 1960s her protests were largely ignored at the corporation on the instruction of the then DG, Hugh Greene. Once Greene departed she began to get a foot-hold. And although she would remain the target of ridicule, she knew how to parlay her position into one of greater influence. Ben Thompson, who has edited her letters, does not underestimate this influence. "From feminist anti-porn campaigns," he writes, "to UK Uncut, and the Taliban and Mumsnet, Mary Whitehouse's monuments are all around us."

The Taliban does seem a stretch. Did Mullah Omar study Whitehouse's notorious blasphemy case against The Romans in Britain before he laid waste to infidels and heretics in Afghanistan? Thompson, alas, doesn't say.

Yet Thompson is on to something. While Whitehouse remained unwavering in her position, the ground around her shifted. When she started out in the 1960s a libertarian idealism suffused the arts and was making headway in society at large. Each new advance against censorship was seen as an unproblematic triumph over oppression. Then gradually some enlightened attitudes edged towards Whitehouse on issues like the commercial sexualisation of children and the sexual exploitation of women. As Thompson notes, although Whitehouse was a true blue Tory, her view of the sex industry shared common ground with Marxist economic critiques. Hers was always the kind of small-mindedness that sensed a bigger picture. If she were alive today she would no doubt see the Jimmy Savile saga, and the panic it has unleashed at the BBC, as a vindication of her warnings.

A further irony of history is that many of those who were prepared to damn this archetypal petty bourgeois busybody in the most venomous terms when she objected to attacks on Christianity were nowhere to be seen or heard during the religious backlash against the Danish cartoons that depicted the prophet Muhammad.

Which raises the intriguing question of whether Whitehouse was loathed for her piety or her identity, the strength of her opinions or the mildness of her methods. The pen may be mightier than the sword but you can't behead anyone with a Biro. Perhaps Whitehouse would have been taken more seriously by her liberal antagonists if her supporters had offered a plausible violent threat.

What is clear is that religious cranks have gained a great deal of wary respect in recent years and, for all her genteel presentation, Whitehouse was a religious crank. She started out in the evangelical spiritual movement Moral Re-Armament and went on to wage a prolonged war against freedom of expression. She knew what was best for society because she knew what God wanted for society. Had conviction been the extent of her weaponry she would have been no more than the epistolary equivalent of a sandwich-board eccentric. But she also had persistence and an instinctive understanding of media mechanics. Thompson is strong on her tactical nous. "One of Mary Whitehouse's favourite tricks," he writes, "was to refer neutrally to 'controversies' she herself had generated as if they were simply historical facts of which all must take cognisance."

She also knew that the media craves characters. She swiftly became Mary Whitehouse within inverted commas  a position to which her numerous chat-show appearances and six-volume autobiography paid handsome testimony. Her letters, however, are less than riveting. They offer many examples of her calculating nature but few clues as to why she struck fear into the hearts of television executives. Despite the odd flash of wit, they are rather tiresome, as letters of complaint  unless you are the complainant  tend to be.

Far more revealing are the mandarin replies from BBC high-ups and politicians, which often betray a disagreeable mixture of managerial anxiety and patrician disdain.

Thompson is more sympathetic. He respects Whitehouse as a cultural phenomenon but is also archly drawn to her value as a social joke. Yet as he reminds us, it's she who has had the last laugh. For the spirit of this patron saint of orchestrated outrage lives on in drummed-up internet campaigns and Twitterstorms and every righteous complaint ever left in an online comment box.

On January 1 1973, Mary Whitehouse wrote to the BBC's director general about the performance of "My Ding-a-ling" on Top of the Pops. The secretary of the National Viewers' and Listeners' Association had received several letters of complaint about Chuck Berry's single. "One teacher," Whitehouse wrote, "told us of how she found a class of small boys with their trousers undone, singing the song and giving it the indecent interpretation which  in spite of all the hullabaloo  is so obvious  We trust you will agree with us that it is no part of the function of the BBC to be the vehicle of songs which stimulate this kind of behaviour  indeed quite the reverse."

I love that "indeed quite the reverse". It was Whitehouse's contention that the BBC should be encouraging mucky little boys to do up their flies, stand up straight and join others in building a Britain staunchly resistant to the dismal depredations of cynical smut.

That, you'll have noticed, hasn't happened. Today, 11 years after Whitehouse's death, cynical smut has become so very nearly ubiquitous and thus so unexceptional to our coarsened sensibilities, the sexual commodification of women's and girls' bodies so commonplace as to pass scarcely noticed, with telly porn accessible at the push of a button, that it is hard to read Ban This Filth!: Letters from the Mary Whitehouse Archive 1963-2001 without thinking that the upright, uptight campaigner had a point.

Should the BBC's function be to improve public morals? Or should freedom of expression, even if that involves broadcasting a once-great rock'n'roll guitarist's wretched foray into the innuendo-laden novelty single genre, always be paramount? And was the "My Ding-a-ling" imbroglio really the right forum for these issues, as old as Plato and still vexed, to be debated?

The then-director general, Charles Curran, thought not. "'My Ding-a-ling'," Curran had written to Whitehouse on 21 November 1972, "begins with such a clear account of the contraption in question including bells, that although the possibility of a double entendre was recognised, we decided that it could be broadcast  We did not think it would disturb or emotionally agitate its listeners and we believe that the innuendo is, at worst, on the level of seaside postcards or music hall humour." That phrase, "contraption in question including bells", is surely worth the licence fee alone.

The exchange was typical of the collection of letters that Ben Thompson has so astutely assembled and comments on so drolly in this book. Here, the bottomless capacity for affront of morally upright, often evangelically Christian, middle England clashes repeatedly with the patrician disdain of those men (and they were overwhelmingly men) who ran the culture industries, be they telly, theatre, cinema, magazines or pornography. Thompson ingeniously suggests that Whitehouse shared much with her punk contemporaries  both were socially excluded, both rebelled against establishment values they detested. Mary as a punk rocker? Not quite. But both she and Johnny Rotten knew how to needle grandees and relished the experience.

But here's the twist. At the end of his Ding-a-ling letter to Whitehouse, Curran wonders "whether the record would have remained in a high position in the charts for such a long time without the publicity attendant upon the publication of your comments." Intriguing point. Perhaps Whitehouse, far from cleaning up society, was instrumental in bringing about the nightmarish scenario she prophesied.

Certainly her complaints could have unintended consequences. On 21 August 1972, Whitehouse wrote to the BBC's head of light entertainment, Bill Cotton, complaining about Top of the Pops giving "gratuitous publicity" to Alice Cooper's "School's Out". "Because of this millions of young people are now imbibing a philosophy of violence and anarchy  It is our view that if there is increasing violence in the schools during the coming term, the BBC will not be able to evade their share of the blame." Cooper sent Whitehouse flowers in gratitude for the publicity her campaigning brought him.

Like Plato, she regarded artistic expression as impermissible when it conflicted with the dictates of a well-ordered polity. On 6 October 1965 she wrote to the home secretary, Sir Frank Soskice, asking whether Peter Watkins's disturbing post-nuclear drama The War Game should be screened on the BBC. "This would seem too serious a matter to be treated as entertainment," she wrote. Artistic expression was thus subsumed by Whitehouse into entertainment, and the proper role of entertainment was to provide wholesome diversion. "Dear Sir," she wrote to the producer of Anglia TV's Survival on 20 August 1970. "May I express our very great pleasure in your truly delightful programme on the beaver?" Please, she urged, repeat it at an earlier time, for it "would fit perfectly into family viewing time".

Whitehouse, Thompson suggests, was an artist who found her voice in trying to silence others'. For instance, when she prosecuted Michael Bogdanov for "procuring persons for an act of gross indecency in a public place" in directing the National Theatre production of Howard Brenton's The Romans in Britain, this led to an 18-month drama of a court case improvised by Whitehouse. That drama involved a media circus, a QC's crisis of conscience, bitter recriminations and the verdict that turned on a thumb being misidentified as an actor's penis. All of this, Thompson suggests, was "little short of a masterpiece"  something he couldn't say of Brenton's leftist agitprop with its homosexual rape scene. The puritan in horn-rimmed specs, here and elsewhere, made Britain even gayer (possibly in both senses of the word) than it would otherwise have been.

Whitehouse resigned as a teacher in 1964 to devote her energies to the Women of Britain Clean Up TV campaign and later the NVALA. She was convinced that the BBC "had become a sounding board for those whose ideas undermine the basis of our Christian faith and our democratic way of life". The satirist Ned Sherrin mused in a Daily Mail interview in 1964 about why she had to give up her job to monitor programmes. "What puzzles me is: what sort of job was she doing that kept her busy at the hour of the night when we're going on the air?" he asked. "I suppose that she must have been on the streets." In the resultant libel case, Whitehouse accepted a "three-figure sum" from Associated Newspapers for the slur.

Her nemesis (or, rather, the first of her nemeses) was Sir Hugh Greene  brother of novelist Graham  who had been the BBC's director general since 1960 and so had overseen the corporation's satire boom and the topical dramas of the Wednesday Play strand. He believed that the BBC's irreverent, anti-deferential, subversive programming policies expressed the very freedoms for which the sacrifices of 1939-45 had been made. A Telegraph correspondent in Berlin in the 1930s and later at Auschwitz shortly after its liberation, Greene was a man who, Thompson argues, "took a dim view of any kind of authoritarian consensus". And, Thompson says, this is just what he found in Whitehouse's campaign. He took the platonic Whitehouse to be an enemy of the open society for which Britain had ostensibly fought.

Unfortunately for Thompson and this book, that freighted ideological battle was never to be joined in letters. Greene devolved replies to her correspondence to his minions. He did, though, congratulate programme makers who elicited complaints from Whitehouse. He took particular pleasure in the sitcom that most scandalised Whitehouse and her followers, Till Death Us Do Part, whose anti-hero, the homophobic, royalist, racist working-class Tory Alf Garnett, held views that one might suspect the NVALA demographic shared. "The amusing thing about Alf," Greene told a Time magazine interviewer, "is the intense fury aroused among those who share his prejudices. The programme offends a great many people  but those one is glad to offend."

But then the Whitehouses were quick to take offence. On 22 July 1969, Ernest Whitehouse wrote to the director general about remarks made about his wife on Quiz of the Week. "The remarks by the panel and attributed to Lord Goodman were that she was 'a hypocritical old bitch'," Mr Whitehouse wrote. "Such can only be classified as gratuitously scandalous if not indeed defamatory of character; what is worse, they were made against a person, who is not in a position to defend herself and mostly barred from TV anyway, by those exhibiting their verbal prowess for money."

The panel thus described sounded like proto-Frankie Boyles, shabbily mocking the weak. Charles Curran (Greene had resigned the previous year) replied on 25 July. During the programme, he explained, one of the show's panellists, the handlebar-moustached MP Sir Gerald Nabarro, had looked at a photograph depicting Lord Goodman (who at the time was a member of a working party studying proposed obscenity laws) and Mary Whitehouse. Curran explained: "Sir Gerald Nabarro, on seeing the photograph, said: 'I think he [Lord Goodman] is thinking 'you hypocritical old bitch'." Curran went on: "We have since spoken to Sir Gerald about your complaint. He was at pains to point out that he is a member of NVALA and that furthermore he supports wholeheartedly the attitude that NVALA has taken towards the proposed obscenity laws." Did the NVALA later shred Sir Gerald's membership card? It's possible.

Mary Whitehouse didn't only fight against the BBC. During the 1980s, unsurprisingly, she was affronted by and complained about Channel 4's output. "I am glad to see the home secretary's unexceptional reply to your unnecessary letter," wrote Jeremy Isaacs, C4's chief executive, in 1984, responding to some dyspeptic jeremiad. She also took on the pornography industry: "Thank you for your letter concerning our bookstall at Crewe Station," wrote John M Menzies on 28 May 1984, after Whitehouse complained about finding a pile of Knave magazines at a level where "almost any child could see and pick it up". "Our policy  is not to sell these magazines to children."

She tried to stiffen the established church in what she thought should be its homophobic resolve: "Will you state publicly and quite specifically," she wrote to the Bishop of Southwark on 22 June 1979, "whether you are endorsing the practices of mutual masturbation common among some homosexuals, and whether you expect the church to do the same and whether you see such practices as the will of God." "Yes, I jolly well am and jolly well do," replied the bishop. I'm kidding. If only he had.

She demanded politicians revise obscenity laws. That prompted a reply from David Mellor, home office minister in 1983, arguing that her proposal that depictions of explicit acts of human urination or excretion be banned would outlaw "a picture of a baby urinating in a nappy advertisement; or a photograph of the mannequin in Brussels which serves as a fountain". Similarly, Mellor argued, the NVALA's proposal to ban depictions of mutilation, flagellation or torture would ban King Lear, certain religious paintings, and the films of Tom Brown's Schooldays and Nicholas Nickleby.

She campaigned against blasphemy and homosexuality, especially when, as in James Kirkup's poem "The Love that Dares to Speak its Name", they came together. Whitehouse privately prosecuted Gay News's editor, Denis Lemon, in 1977 for publishing Kirkup's necrophilic account of sexual assault on Christ's crucified body. After Lemon's conviction for blasphemous libel, she received a letter from the clerk of the Scottish Free Presbyterian Church Synod, informing her of its unanimous motion thanking Whitehouse "for your unflinching stand against Sodomites in a recent court case".

For Whitehouse, taking offence and imputing mucky motives to those who didn't share her worldview weren't so much tactics as irrepressible ways of being. In 1990, she was sued for libel by Dennis Potter's mother. During an interview with Dr Anthony Clare on his Radio 4 series In the Psychiatrist's Chair, Whitehouse had claimed that Margaret Potter had "committed adultery with a strange man and that the shock of witnessing this had caused her son to be afflicted" with the skin disease psoriasis. Whitehouse thereby confused a storyline from Potter's The Singing Detective with the playwright's life. No doubt her misdiagnosis and jejune psychosexual analysis was prompted by her loathing for Potter's TV drama, which she believed had "made voyeurs of us all". Similarly, perhaps, TV made Whitehouse a voyeur, though sometimes not a discerning one.

What is Whitehouse's legacy? "She was not the last of a dying breed," argues Thompson. "From feminist anti-porn campaigns to UK Uncut, and the Taliban to Mumsnet, Mary Whitehouse's monuments are all around us." Not quite: the Taliban, unless I misunderstand recent geopolitics horribly, owe nothing to Whitehouse. It remains a moot point, though, whether she would have relished recreating something like the Taliban's culturally threadbare theocracy here.