By David Edgar

One striking aspect of the 1968 and post-1968 generation has been overlooked in the current nostalgia fest.

Despite Robert Frost's stern warning against the dangers of youthful idealism ("I never dared to be radical when young, for fear it would make me conservative when old"), remarkably few of those formed by 1968 and its aftermath have moved to the right in middle age. That is, until now.

In the same way that a surprising number of Thatcher and Reagan's key thinkers were former communists, the ideological campaign for the war on terror abroad and against multiculturalism at home has been dominated by people who were formed by the student revolt, feminism and anti-racist movement of the 1970s. As with the political defectors of the past, their critique of the left is validated by personal experience. Just as past generations sought to reposition the fault-lines of 20th-century politics (notably, by bracketing communism with fascism as totalitarianism), so, now, influential writers seek to redraw the political map of our own time. And, intentionally or not, they are undermining the historic bond between progressive liberalism and the poor.

I became interested in the politics of defection in the late 1970s. I'd written a play about the far right (Destiny), but as the National Front crashed to ignominious defeat in 1979, it was clear that its thunder had been stolen by a resurgent conservatism that owed much of its passion and its principles to deserters from the left. As the death-agony of the 1974-79 Labour government unfolded, former socialists and communists contributed to proto-Thatcherite tirades with titles like "The Future that Doesn't Work" and "An Escape from George Orwell's 1984". In 1978, former leftwingers such as Kingsley Amis, Max Beloff, Reg Prentice, Paul Johnson and Alun Chalfont anthologised their apostasy in a book proudly titled Right Turn.

In my play about defection (Maydays, produced by the RSC in 1983), I speculated about how the British class of '68 might move to the conservative right. Essentially transposing the experience of earlier generations into the 70s, I don't think my central character's trajectory was implausible. In France, Bernard-Henri Lévy and other nouveaux philosophes had provided a vocabulary of retreat for the veterans of the Paris events of May 1968. Some American popular radicals had fled to business (Jerry Rubin) or to the religious right (Eldridge Cleaver), and former Ramparts editor and Black Panther supporter David Horovitz was to mount a 1987 conference, Second Thoughts, at which former 60s radicals such as Michael Medved and PJ O'Rourke confessed and renounced their errors. Nonetheless, most of the leading figures of the period - from Tom Hayden, Todd Gitlin and Bernardine Dohrn in America via Danny Cohn-Bendit in Germany to Tariq Ali, Robin Blackburn and Sheila Rowbotham here - have remained faithful to their previous ideals. And while Alan Milburn, Alan Johnson, Alistair Darling and Stephen Byers have clearly moved a considerable distance since their days in or about the Trotskyite far left, they would doubtless claim to be pursuing a drastically revised version of the same, socially progressive agenda. Until very recently, almost everybody disillusioned with the far left felt there was still a viable near left they could call home.

Now, that appears to be changing. Bookshop shelves are not quite yet groaning with defection literature, but Nick Cohen (What's Left?), Andrew Anthony (The Fallout), Ed Husain (The Islamist) and Melanie Phillips (Londonistan) are all self-confessed deserters (Phillips wears the "apostate" label with pride). Although Martin Amis was never part of the revolutionary or communist left (and attacked both his father and his friend Christopher Hitchens for so being), The Second Plane is an assault on the kind of liberal, literary intellectuals among whom Amis has moved throughout his life. And although Cohen, Anthony, Phillips et al have poured particular vituperation on leftwing playwrights (David Hare and Harold Pinter in particular), they have now been joined by one - David Mamet, who last month wrote a piece for the Village Voice entitled "Why I am no longer a 'brain-dead liberal'" (he no longer believes that "people are basically good at heart"). Like previous generations, these defectors have been there, done that, and can now bear witness to their former misbeliefs. In so doing, they are joining a club with an extensive membership. Most of the radical and progressive achievements of the 20th century - including the Russian revolution - were brought about by an alliance between the oppressed and the intelligentsia, and a good proportion of them - particularly the Russian revolution - were followed by disappointment and desertion. For some, disillusion set in as early as 1921, when the Bolsheviks suppressed a sailors' uprising at Kronstadt, the port of St Petersburg and cradle of the October revolution. Subsequent "Kronstadt moments" included the Stalinist purges of the 1930s, the 1939 Nazi-Soviet pact, the neo-Stalinist show trials in eastern Europe in the early 50s, Khrushchev's exposure of Stalin's crimes in February 1956 and the Soviet invasion of Hungary in November of that year.

As a result of these crises, ex-communist writers such as Arthur Koestler and Stephen Spender moved to the liberal centre. Others, like WH Auden, withdrew from political involvement altogether. For many, like the American poet and bohemian Max Eastman and the fellow-travelling novelist John Dos Passos, the cold war provided a changing room from which they emerged - with new stars in their eyes - as full-blown, traditionalist conservatives.

The events of 1956 changed the rules of membership of the ex-communist club in two ways. The creation of a self-consciously non-Stalinist New Left gave people disillusioned with communism somewhere else to go. On the other hand, the subsequent activities of the New Left became a recruiting agency for the right among older radicals, socialists and even liberals. For ex-communist Kingsley Amis, opposition to the expansion of higher education ("more will mean worse") was the first of many Conservative causes which transformed the author of Lucky Jim into a Thatcherite cheerleader. Similarly, what became the Reagan coalition was given considerable intellectual ballast by a group of New York intellectuals surrounding ex-Trotskyite Irving Kristol, for whom the hippy counter-culture, Black Power and later the women's and environmental movement demonstrated the infantilism and nihilism of the New Left. Self-defined as "liberals mugged by reality", Kristol, Norman Podhoretz, Nathan Glazer and Daniel Bell were genuinely neoconservatives, having previously been revolutionaries (Kristol), radicals (Podhoretz, Glazer) or at the very least democratic progressives.

As former victims of political delusion, these defectors claim a unique authority. But there is something quite particular about spending the second half of your life taking revenge on the first. Inevitably, however complete the conversion, what defectors think and do now is coloured by what they thought and did before. Most people who leave the far left do so because of their experience of far-left organisations: their authoritarianism and manipulation, their contempt for allies as "useful idiots", their insistence that the end justifies the means and that deceit is a class duty, their refusal to take anything anyone else says at face value (dismissing disagreement as cowardice or class treachery) and, most of all, their dismissal as "bourgeois" of the very ideals that draw people to the left in the first place. As Spender wrote in The God that Failed (1949), "the communist, having joined the party, has to castrate himself of the reasons which made him one".

But, often, something else is going on. Frequently, there is a sense among defecting intellectuals that it's not just the party that has let them down. Most people move left either because they are outraged by the victimhood of the oppressed (Spender's distress at men and women "sealed into leaden slums") or because they are inspired by the left's revolutionary ardour (as many of my generation were by the Black Panthers and the Vietcong). The discovery that the poor do not necessarily respond to their victimhood with uncomplaining resignation is as traumatic as the complementary perception that they don't always behave in a spirit of selfless heroism.

Hard enough to be fooled by the party; even harder to accept that you deluded yourself into believing that the poor are, by virtue of their poverty, uniquely saintly or strong. No surprise that this realisation turns into a sense of personal betrayal, which turns outwards into blame.

One obvious result of this is the tendency of ex-radicals to become very conservative indeed, a tendency satirised by Edmund Wilson in his quip about John Dos Passos: "On account of Soviet knavery / He favours restoring slavery". Dos Passos was not the only American Marxist to pole-vault the cold-war liberal centre and land in the arms of William F Buckley's high conservative National Review. Initially claiming that he still believed in the end of working-class emancipation, former Trotskyite Max Eastman quickly turned on "mush-headed liberals" who "bellyache" about civil rights; for former beat critic and latter neoconservative Podhoretz, homosexuality was a death wish and feminism a plague.

Above all, the reality that neocons felt mugged by was the moral inadequacy of the poor. Kristol's manifesto On the Democratic Idea in America blamed the free market for encouraging unreasonable appetites in the working class; as Robert Nesbit put it, "to allay every fresh discontent, to assuage every social pain, and to gratify every fresh expectation".

Like Eldridge Cleaver, the neocons argued that the welfare state had turned the poor into parasites; James Q Wilson asserts that, in the black community, welfare became for black women what heroin was for black men. For Podhoretz, far from being "persecuted and oppressed", the blacks he knew were doing the persecuting and oppressing.

The directness and lack of apology in neoconservative polemic is a result of the fact that its authors had discharged the same ordnance in the opposite direction, and knew the likely weight and calibre of the returning fire. Most political defectors leave the left because its authoritarian practices stand in such stark contrast to its emancipatory ideals. For many, however, there is a double paradox: on opening their suitcase at the end of the journey, they find not just that the libertarian ideals they left the left to preserve have gone missing, but that the only thing remaining is the very cynicism and ruthlessness which they left the left to escape.

So, as on the far left, there is a tendency to see the world in stark, binary terms. Kingsley Amis once admitted that "it's all pretty black and white to me now. If you decide, as I have, that there are only two sides to the argument, then it's all quite simple." Kristol insists that environmentalists aren't really interested in clean air or clean water; what they're really after is authoritarian political power. And a condemnation of the practice of radicals and revolutionaries justifies the abandonment of the groups they seek to defend. For neocon Nathan Glazer, 60s radicalism was "so beset with error and confusion" that even its mildest manifestations - such as affirmative action for African Americans - had to be swept away.

Is this pattern reflected among those defectors for whom the "Kronstadt moment" was 9/11? Certainly, Husain's The Islamist describes a progression towards and then away from the non-jihadist but pro-Caliphate Hizb ut-Tahrir, which will be familiar to any reader of defection literature; he is now working with the Conservative thinktank Civitas. Commentators Nick Cohen, David Aaronovitch and Andrew Anthony all had left-wing parents, and were involved in political campaigning around race, gender and class in the 1970s (Aaronovitch was one of Manchester University's notorious University Challenge team, who answered "Marx", "Lenin" or "Trotsky" to every question). Although none of them has abandoned the whole progressive package, their main target is a left-liberal intelligentsia, which, as they see it, opposed the overthrow of a fascist dictator, Saddam Hussein, and is now in an unholy Faustian alliance - justified by modish, postmodern cultural relativism - with the far right.

The far right in question is not the BNP, but political Islamism, represented by those main Muslim umbrella organisations that are seen to have links with Islamists in Muslim countries, particularly those who joined the coalition that organised the demonstration on February 15 2003 against the invasion of Iraq. And, as no one is suggesting that the Socialist Workers Party, or its fellow travellers in what Aaronovitch calls "the bruschetta crowd", is using the anti-war alliance to pursue a hidden, anti-feminist, homophobic and theocratic agenda, it initially appears that the dupers are conspiratorial Islamists and the dupees the naively innocent socialists who marched beside them. Just like the "useful idiots" of the 30s, they are giving aid and comfort to Muslim extremists, in the deluded hope (to quote Cohen) that the Islamists will "shake themselves and say, 'fair enough, we realise that now you've addressed our root cause, we don't want a theocratic empire after all'".

No one on the progressive liberal left can be comfortable with any of the religions of the book, particularly when literally applied. And those of us who dismissed the oppression of women and gay people as "secondary contradictions" in the early 70s are correctly wary of putting those issues on the back-burner now. Certainly, the progressive left is in alliance with a group whose traditional views run counter to some central planks of its platform. Twenty-five years on from Maydays, I have written a new play (Testing the Echo), which is partly about the temptation - on these understandable grounds - to reject any kind of religious affiliation, to brand fundamentalist Islam as brown fascism, and (thereby) to abandon an impoverished, beleaguered and demonised community.

For, let's be clear, the alliance to which the new defectors object - the alliance enabled by a multiculturalism that sought to give visibility and confidence to entire communities - is not just between a few deluded revolutionaries and the odd crazed Muslim cleric. Martin Amis denies he's declaring war on the world's 1.3 billion Muslims, but his "thought experiment" about meting out collective punishment on Muslims (travel restriction, deportation, strip searching) "until it hurts the whole community" makes no distinction between followers of Hizb ut-Tahrir and the man in the Clapham mosque.

Cohen is careful to point out that "Islamism has Islamic roots", and, clearly, the group that he dubs the "far right" goes beyond the adherents of Jamaat-e-Islami. It's also a group that - defined in the old-fashioned way as Pakistanis and Bangladeshis - remains at the bottom of the socioeconomic heap. As Trevor Phillips pointed out in his "sleepwalking into segregation" speech, made after 7/7, a Pakistani man with identical qualifications to a white man is still going to earn £300,000 less in his lifetime.

It is also a group that suffered, particularly during Cohen, Aaronovitch and Anthony's formative years. Throughout the 70s and 80s, Paki-bashing created an image of Britain's south Asian communities as a traditionally submissive group, victimised by unwarranted aggression. For some, this image was complemented by admiration for groups such as the Bradford 12, who sought to defend their communities against fascist attack, and won the right to do so in court. When, in 1989, Bradford's Pakistanis found a sense of self-confidence and identity through burning books rather than banks, it's no surprise that liberal progressives who had supported, maybe even pitied, that community felt a sense of betrayal. In their books, Cohen and Anthony frequently point out how people on the left grow bitter when the poor fail to live up to the romance of unbridled heroism or untainted victimhood. They don't fully take into account the effect of that delusion on themselves.

Many of the usual pathologies of defection can be detected in the current crop. The attack on multiculturalism - so often sold as a reassertion of Enlightenment principles - often masks a distinctly unenlightened reassertion of hierarchic and traditionalist thinking. Despite his defence of women's and gay rights against Qur'anic scholars, a distinct strain of hostility to the sexual gains of the 60s runs through Cohen's What's Left?: he blames the anti-racists and sexual reformers of the 60s for dissolving "the bonds of mutual support", dips more than a toe into the Daily Mail's critique of the welfare state (breaking up families, privileging immigrants), and blames the Respect party for Pakistani and Bangladeshi unemployment.

Martin Amis's elegant prose shouldn't blind us to his seeming obsession with the Muslim birth rate as a "gangplank to theocracy" ("Has feminism cost us Europe?" he asked in an Independent interview). David Goodhart, editor of left-leaning Prospect magazine (who describes the 60s as "the decade that sharply eroded authority and constraint"), argued in his pamphlet Progressive Nationalism for a two-tier welfare system, the teaching of imperial history in schools, the creation of a migration and integration ministry, the raising of citizenship test hurdles, the reassertion of the monarchy and the army as nationally binding institutions, the banning of certain forms of dress from public buildings and the reintroduction of conscription. That several of these proposals are now government policy is an indication of how Gordon Brown's golden thread of British liberties has thickened into what looks more like a whip.

Most importantly, the culture of betrayal has blinded contemporary defectors to the significant achievements of the alliance between British Muslims and the left. Along with Phillips, Cohen and the New Statesman's Martin Bright, Anthony is preoccupied with the Muslim Council of Britain and its spokesman Inayat Bunglawala, quoting his remark that the campaign against Salman Rushdie's The Satanic Verses brought Muslims together and "helped develop a British Muslim identity".

In fact, Bunglawala's attitude to Rushdie goes to the heart of whether the progressive-Muslim alliance is a genuine conversation or the contemporary equivalent to the Nazi-Soviet pact. In a Guardian article last June, he reiterated the importance of the anti-Rushdie campaign in building self-confidence among a small, isolated, beleaguered and frequently victimised community, but went on to "readily acknowledge we were wrong to have called for the book to be banned". Now, he confesses, "I can better appreciate the concerns and fear generated by the images of book-burning in Bradford and calls for the author to be killed". Not least because, as he wrote in response to a critical blog, the same laws that allowed Rushdie to write The Satanic Verses protects the rights of Muslims to say what they think, too.

Support for human rights legislation that protects the rights of religious as well as sexual minorities is controversial within the Muslim community, as are other examples of supposedly diehard Islamists responding to liberal criticism. For example, the MCB came under fire when it decided - not before time - to participate in Holocaust Day ceremonies. Azzam Tamimi is a leading member of the main Muslim organisation in the Stop the War Coalition, the British Muslim Initiative, a group much reviled for its close ties with the Egyptian Muslim Brotherhood and its Palestinian equivalent, Hamas. Tamimi's book on Hamas (published in America as Hamas: A History from Within) contains a sustained critique of Hamas's constitution, its treatment of the Jews, and its quotation of the tsarist antisemitic forgery the Protocols of the Elders of Zion. Another leading member of the BMI, Anas Altikriti, points out that the Qur'an says nothing about homosexuality beyond relaying the biblical story of Sodom and Gomorrah (and, for that matter, does not call for the execution of apostates). Altikriti negotiated for hostage Norman Kember's release in Iraq, campaigned against escalating protests over the Jyllands-Posten cartoons in Denmark (while sympathising with Muslim anger against them) and argues that, unlike the British government, he has been fighting separatist Muslim extremism since long before 1997.

Despite the drumbeat of demonisation by media and politicians, these and other Muslim leaders are increasingly open to the argument that their shared interest in universal human rights trumps what we rightly regard as illiberal beliefs. They are, in other words, going in precisely the opposite direction from that which their detractors describe and predict. Are they really (to use Hitchens's formulation) to be anathematised as "fascists with an Islamic face"?

All of the great progressive movements of the 20th century in the west - solidarity with republican Spain, the building of welfare states, the civil rights movement in the southern United States, the war against apartheid in South Africa - were led by an alliance between progressive intellectuals and the victims of oppression. The civil rights movement in particular allied secular Jews (often with communist backgrounds) from the north with black Christians in the south. The difficulties of that relationship were demonstrated when - after victory was largely won - blacks asserted the need for an all-black leadership of one of the main civil rights groups. Later, feminists properly criticised the leaders of the Black Panthers for the sexism of both their political practice and personal behaviour. Despite all that, does anyone think the creation of the alliance which successfully desegregated the American south was a mistake?

Whether they like it or not, the current defectors are seeking to provide a vocabulary for the progressive intelligentsia to abandon the poor. So, for civil libertarians, the divide is no longer between left and right, but between authority and personal liberty. For atheists, it is between secularism and religious belief. For some American and European feminists, it is between women's rights and a multiculturalism that validates Muslim patriarchy. For a number of former leftwingers, it is between the social solidarity of a conservative working class and the demands of multicultural newcomers.

What all these fault-lines have in common is that they pit progressives against the group that is under the most sustained political attack, here and abroad, and that those who draw them include people who have the authority of the convert, having seen the error of their ways. It behoves those of us who have also been there and done that, not to defend the indefensible, but to protect the vocabulary of alliance that has done so much good in the past and is so necessary now.

David Edgar is a British playwright.
© 2008 The Guardian