Everyone knows Michael Ignatieff. Some first encountered him during the late '70s when his painstaking historical analyses of the evolution of the British penal system provided a valuable empirical complement (some would say antidote) to Michel Foucault's Discipline and Punish. Others will have come to respect him for his novels, family memoirs, or his outstanding biography of his great hero, Isaiah Berlin. Many more will remember the suave, querulous, intellectual contributions he made to BBC 2's culture-based talking shop, The Late Show. By the time that programme stuttered to a close in the mid-90s news of his fame had even made it back to his country of birth. In 1997 MacLean's magazine included him in its 'Top Ten Canadian Who's Who' and four years later exultantly promoted him to Canada's 'Sexiest Cerebral Man' because of "his made-for TV looks and effortless eloquence".

What so endeared Ignatieff to the thinking classes was his cosmopolitan liberalism. His Russian family background, North American childhood and easy mastery of several languages seemed to qualify him as a citizen of the world. It was not too surprising, therefore, when he set off for what he described as "the landscapes of modern ethnic war" - Serbia, Croatia, Bosnia, Rwanda, Burundi, Angola, and Afghanistan - in search of an answer to a classic liberal question: why do we in the west feel that we have a moral obligation to become embroiled in the internal conflicts of distant lands? His answer helped to transform him into a leading figure in the human rights movement. We could, he argued, only overcome the ethnic particularism that lay behind so many of today's conflicts by treating others -whatever their religion, class, gender, race - as rights-bearing equals rather than as members of a group. Such whole-hearted advocacy of human rights meant that he was a natural choice for the prestigious post as Carr Professor of the Practice of Human Rights in the Kennedy School of Government at Harvard University.

Yet this success story, of a liberal intellectual coming into his own, is rapidly turning very sour. Instead of being regarded as a champion of human rights, Ignatieff is now being seen, in the words of one senior academic, as 'a virus in the human rights movement'. Until recently this might have been written off as an intellectual spat. But recent events look likely to precipitate a full scale divorce between Ignatieff and his former colleagues.

It all began with an article on torture by Conor Gearty, Professor of Human Rights Law at the LSE, in the February 2005 edition of the Index on Censorship. Gearty's concern was to show the process by which a number of well-meaning liberal intellectuals and human rights lawyers had handed Donald Rumsfeld "the intellectual tools with which to justify his government's expansionism". He was particularly exercised by the manner in which such people had created a climate in which even torture could be condoned. One of the well-meaning liberals cited by Gearty in this context was Michael Ignatieff.

Ignatieff's response was as violent as it was unexpected. The harm done to his reputation by the article, he insisted, was so great that it could not even be remedied by the chance to rebut. He had no alternative but to resign immediately from the editorial and advisory board of the magazine and request that any syndication of Gearty's piece be withheld. This was "an issue of principle".What was the background to this outburst? Why exactly was Ignatieff so offended by an academic article? What does his response say about his present standing within the human rights movement?

Let us first examine the magazine. Index on Censorship was founded in 1972 by a group of writers, journalists and artists committed to chronicling free expression abuses wherever they occur. Michael Ignatieff is himself a member of its high profile editorial and advisory board, and its long list of distinguished contributors includes Vaclav Havel, Salman Rushdie, Doris Lessing, Noam Chomsky and the late Ken Saro-Wiwa.

For the magazine's first edition this year, the editor-in-chief, Ursula Owen, invited Stan Cohen, Professor of Sociology at the LSE, to guest edit a special section on torture. Its cover featured a disturbing image of half-naked blindfolded and shackled victims and the legend 'TORTURE: A USER'S MANUAL'. Stan Cohen himself wrote on the 'slippery slope that leads from Guantanamo to Abu Ghraib', while Conor Gearty's essay was headlined: 'With a little help from our friends. Torture is wrong and ineffective. So why is it making a comeback?'

Gearty began by considering the social and cultural ingredients that might allow a liberal democracy to forgo its traditional commitment to human rights to an extent that led it finally to condone torture. First into the mix was a category of persons he described as 'Rumsfeldians', individuals "distinguished by their determination to permit, indeed to encourage, the holding of suspected 'terrorists' or 'unlawful combatants'…in conditions which make torture, and inhuman and degrading treatment well-nigh situationally inevitable."

But Rumsfeldians could not transform liberal discourse on their own. They needed a great trauma like 11 September 2001 on which to feed and, crucially, they also needed some ideological support from apologist intellectuals and lawyers which would help to explain why there is no conflict between torture and our liberal code of laws.

It is at this point that Gearty rounds on Michael Ignatieff, who he describes as "probably the most important figure to fall into this category of hand-wringing, apologetic apologists for human rights abuses." What exactly had Harvard's Professor of Human Rights done to deserve such censure?

For the answer, we need to go back to the arguments that Ignatieff, following his tour of conflict zones, began to develop about the need for western humanitarian interventions in failed or terrorist-dominated states. He was far from alone in adopting this interventionist stance. Many other intellectuals and human rights activists found it possible to agree that there were circumstances under which an imperialism carried out in the name of human rights in such areas of conflict as Bosnia, Kosovo, and Afghanistan was not only defensible but positively to be welcomed.

But many such allies felt far less comfortable when Ignatieff went on to use the same argument to justify the second invasion of Iraq in March 2003. To go along with Ignatieff now meant bypassing the United Nations, ignoring the entreaties of former close European allies, and overlooking the failure to find any weapons of mass destruction. As the death toll mounted in Iraq, it also became necessary to argue that such extreme sacrifices were worth making if they contributed to the end of 'terrorism'.

Ignatieff confronted such moral reservations in 2004 with The Lesser Evil: Political Ethics in an Age of Terror. His preface outlined the key questions he would be addressing: "When democracies fight terrorism, they are defending the proposition that their political life should be free of violence. But defeating terror requires violence. It may also require coercion, deception, secrecy, and violation of rights. How can democracies resort to these means without destroying the values for which they stand? How can they resort to the lesser evil without succumbing to the greater?"

Even before the publication of The Lesser Evil, Ignatieff had attracted some powerful, if predictable, enemies. His justifications for the Iraq war had incensed many radicals. Michael Neumann, Professor of Philosophy at Trent University in Ontario, described the imperialist thesis as developed in Ignatieff's Empire Lite (2003) as "a web of foolishness, error and confusion". The argument that America was still the world's best hope for the spread of liberal democratic ideas was "built on sand" and his proposals for nation-building when stripped of "claptrap" were deeply flawed. They amounted, Neumann wrote, to this: "The US should, having first consulted its own interest, occupy 'failed states' and suppress disorder. Then, over what Ignatieff repeatedly emphasises is a long period of time, Americans are to teach these little folks abut judicial procedure, democracy and human rights. Then Americans will help their apt pupils to create sustainably democratic institutions."

But with the publication of The Lesser Evil in 2004, and a series of articles which expanded on aspects of the book's arguments in the New York Times, he also began to incur the wrath of liberals and, perhaps more significantly, former colleagues in the human rights movement. The critics began to line up. In a 2005 article called 'Exporting Democracy, Revising Torture: The Complex Missions of Michael Ignatieff', Mariano Aguirre concentrated particularly upon the seven pages in The Lesser Evil which dealt with the question of torture.

In this brief section, Ignatieff turns to the so-called 'ticking-bomb cases' where torture might be the only way to extract information from terrorists which could save human lives. He cites Harvard Law professor Alan Dershowitz, who had contended that "whatever we might think about torture in the abstract, the pressure to use it in cases of urgent necessity might be overwhelming. The issue then becomes not whether torture can be prevented but whether it can be regulated."

Ignatieff rejects this argument - "as an exercise in the lesser evil it seems likely to lead to the greater" - along with other justifications for the use of torture by democratic societies. Nonetheless - and this is critical to the argument that was to develop - he does go so far as to suggest forms of duress that might be permissible. These include "forms of sleep deprivation that do not result in harm to mental or physical health, and disinformation that causes stress."

Aguirre describes this style of argument as 'and yet and yet'. Ignatieff is "absolutely in favour of the principles and the defence of human rights, and yet, and yet, if a terrorist has valuable information about a biological weapon that is going to explode in New York, then maybe the security forces could use some level of force on him. Thus, the director of the Carr Centre for Human Rights Policy at the Kennedy School of Government in Harvard University becomes a sort of Bruce Willis figure."

This 'and yet and yet' approach, suggests Aguirre, is just what the US government needs as a justification for its current breaches of human rights. "Ignatieff considers himself a liberal, so sometimes he criticises the Bush administration. And he is an intellectual, so he has doubts about almost everything and airs them with the liberal readers of the New York Times. But in the end he shares the US government's vision of the violent and compulsory promotion of democracy, the war against terrorism and the use of instruments, for example torture, which are apparently in need of revisionist treatment." In these ways, "he has established a sort of rational framework for democratisation by force and also for the revision of our understanding of human rights."

But how is that revision managed? Gearty in his Index essay suggests that it depends upon a simple verbal shift: "The trick…is to take the 'human' out of 'human rights'. This is done by stressing the unprecedented nature of the threat that is currently posed by Islamic terrorism, by insisting that it is 'a kind of violence that not only kills but would destroy our human rights culture as well if it had a chance'. In these extraordinary circumstances, 'who can blame even the human rights advocate for taking his or her eye off each individual's puny plight, for allowing just a little brutality, a beating-up perhaps, or a touch of sensory deprivation?'. But once intellectuals do open this door then scores of Rumsfeldians pour past shouting 'me too' and (to the intellectual's plaintive cries of protest) 'what do you know about national security - go back to your class work and the New York Review of Books'."

Ignatieff is the best exemplar of this type of intellectual because of his apparently total commitment to the idea that we are now faced with 'evil' people and that unless we fight evil with evil we will succumb. It is precisely because we are democratic and special that, in Ignatieff's words "necessity may require us to take actions in defence of democracy which will stray from democracy's own foundational commitments to dignity." So occasional lapses in human rights can be excused as lesser evils. Gearty suggests that this is already providing an escape clause for those who torture. "If Abu Ghraib was wrong then that wrongness consisted not in stepping across the line into evil behaviour but rather allowing a 'necessary evil' (as framed by the squeamish intellectuals) to stray into 'unnecessary evil' (as practised by the not-so-squeamish Rumsfeldians)."

At no point does Gearty suggest that Ignatieff condones or favours torture. Indeed, for him to do so would be to destroy his entire argument: that intellectuals like Ignatieff are providing a moral framework for such practices by introducing concepts of 'good' and 'evil' into a previously secularised domain of discourse. Once this shift has been made, Gearty argues, we can say goodbye to the notion of universal human rights. After all, why should we extend the same rights to those who are good as those who are evil? "The wonder is not that we good guys abuse their human rights, but that we continue to use such language in relation to them at all, recognise that they have any residual human rights worth noticing."

Gearty and Aguirre are by no means alone in their concern about the manner in which Ignatieff's argument in The Lesser Evil provides a framework within which torture might be contemplated by liberals. A particularly hostile review in the New York Times in July 2004 by international relations professor, Ronald Steel, began with this acerbic summary of Ignatieff's thesis: "Michael Ignatieff tells us how to do terrible things for a righteous cause and come away feeling good about it." Ignatieff may tell us that the lesser-evil position lies in never losing sight of the "morally problematic character of necessary measures," argues Steel, "but is it really true that an evil act becomes lesser simply because it is problematic? Does suffering a twinge of bad conscience justify what we do in a righteous cause? It is comforting to think so, but saying 'this hurts me as much as it does you' is neither true nor considered an excuse."

What most of these critiques of The Lesser Evil have in common is the uneasy sense that Ignatieff, despite his constant cautionary remarks and reluctant asides ('and yet and yet') is in the dangerous business of providing rationalisations which only need to be stretched a further inch or two before they become 'permissions' for those who feel that human rights are contingent or expendable in the war against terrorism.

But none of this explains how Ignatieff could have interpreted Gearty's Index on Censorship essay as an assertion that he was in favour of torture, nor the intemperance of his email to Ursula Owen, a friend of long standing. Gearty, he insisted, in spite of the clear textual evidence to the contrary, had not read what he, Ignatieff, had written. By suggesting that he was in favour of torture he had delivered a blow to his reputation of such severity that he must now ask for his name to be removed from the editorial board of the magazine. He went on to ask Owen to ensure that the piece would not be syndicated elsewhere because it is 'factually false'. If it had already been sold then she must send a copy of this present letter to the editors concerned in the hope that this will help "to undo the damage you have already done to my reputation".

Ignatieff does admit that he cannot expect any "immunity from criticism" as a friend of the magazine, but surely any "person, friend or not, whose views and moral reputation are attacked in this form is entitled to elementary exercises of editorial due diligence. If your editorial staff had spent five minutes checking Mr Gearty's insinuations against the text of my book, they could have spared me this insult to my reputation and might have protected your editorial reputation as well."

Owen replied to Ignatieff regretting that Gearty's piece had caused him quite so much distress. She had realised that he might like to respond to the article but never expected him to be so outraged and insulted as to reject the standard form of academic response. Gearty had not accused him of supporting torture, on the contrary, he specifically says of Ignatieff that 'he does not approve of the use of torture'. All he had said was that Ignatieff's position provided a moral framework for others to do so. "It seems to him that to hold such a position is to render less than definitive the accompanying rejection of torture." She concluded by hoping that Ignatieff would change his mind and reply to Gearty's piece in the next edition of the magazine.

Gearty was very satisfied with this response. "I think your summary is exactly right…the piece…is not about the torturers per se but about liberals whose position leaves room for others, more brutal than them to act." But he was clearly still stung by the severity of Ignatieff's attack. "I think [Ignatieff] should be a bit more specific about what exactly in the text so misrepresents his position, in particular where it is 'factually false'. This is a very serious allegation to make against me. …On its face it is defamatory."

Ursula's response failed to have a calming effect. Ignatieff replied promptly. "The moral framework claim is not an argument but an insinuation that proceeds to link me with others, as you say 'more brutal' than myself'. This is what is called guilt by association, and if you cannot see that this is how you and he are arguing, I cannot argue with you."

The feeling that further argument was fast becoming pointless was not confined to Ignatieff. If he was unable to tell or to accept the difference between an opinion and an insinuation then there seemed nowhere for the debate to go. As Gearty himself put it in a further email to the editor: "As for answering him, well he has said nothing yet. Perhaps he will treat my opinion seriously, in which case I will have a chance to reply. But I can't reply to mere vulgar abuse of which there has been a great deal, so far anyway."

Neither could Ignatieff obtain satisfaction elsewhere. After the first response from the editor he turned to the guest editor of the torture edition, Stan Cohen, another long-standing friend, and expressed the hope that he at least had not aligned himself with those on the magazine who wished to harm his reputation. Cohen immediately wrote back, gently averring that he regarded Michael's reputation as too intact to require any such protection. Neither could he agree that the article had been "a vindictive attack on [Ignatieff's] moral character, nor evidence of editorial negligence, nor a factual distortion". I am sure you are wrong in refusing to publish a response to the article. I very much hope you will change your mind."

There is one word which resonates throughout this episode - 'reputation'. Ignatieff uses it four times in his original letter of complaint and then returns to the subject again in his correspondence with the guest editor.

To some, this concern about 'reputation' is best explained by a bizarre development in Ignatieff's career path: his apparent new interest in pursuing political office in his home country of Canada. When this rumour first began to circulate there was widespread scepticism. But this was soon swept aside by the proliferation of 'informed' newspaper articles on Ignatieff's new ambitions. "If the political supporters of Michael Ignatieff have their way," wrote the Boston Globe on 19 July this year, "the human rights scholar and journalist may soon abandon his post as director of Harvard's Carr Centre for Human Rights Policy and enter the political fray." Neither would Ignatieff confine himself to running for parliament at the next Canadian election. "Power brokers have recruited Toronto-born Ignatieff to return to Canada … with the intention of grooming him to succeed Prime Minister Paul Martin." This theory has been reinforced by the recent announcement that Ignatieff is leaving Harvard to take up a year-long post at the University of Toronto. The Toronto Star on 26 August, suggested this is a prelude to a bid for leadership of the Liberal Party. Many Canadian pundits have been hailing Ignatieff, with his looks, charm and intelligence, as a liberal gift from heaven: another Pierre Trudeau.

Not everyone was so excited. Internet discussion forums revealed serious doubts about Ignatieff's credentials for such a job. Some objections were predictably crude. "This asshole has some nerve; leave the country for 30 years to take the cushy job at Harvard, and then this prick has the auducity (sic) to come crawling back expecting to be Prime Minister?" Others were less than excited by his political record. "Mr Ignatieff, professional mental gymnast and idea contortionist, lost his Canadian moorings long ago - about the same time he lost his ethical moorings and set out his shingle as 'mind for hire'." And then there was the inevitable: "In his writings for a US audience, he has acted as an apologist not only for the invasion of Iraq, but also for torture."

So could political ambition, the desire to have a clean public image, be an adequate explanation for Ignatieff's over-dramatic reaction to Gearty's carefully-reasoned, if provocative, article in Index? After all, he had not reacted half as aggressively to harsher evaluations of his writing on torture in other more widely circulated publications. It's true that his original letter of complaint spoke of the "uniquely painful shock" of being called "one of torture's new best friends" in a magazine in which he was listed on the editorial and advisory board. But his association with the magazine might have equally well inclined him to accept what Gearty had to say in good faith and encouraged him to sit down and compose an adequate response to the alleged misrepresentations. Why the dramatic resignations and the sweeping attacks upon Gearty as a purveyor of the "factually false"?

There is a more subtle explanation for the outburst. Ignatieff has used Freudian insights to good effect in the past. In Warrior's Honour he employs what Freud called 'the narcissism of small differences' to explain some of the irrationality that has characterised recent ethnic conflicts. Perhaps, therefore, it is appropriate to suggest that there might be some sign of 'reaction formation' in his most recent fulminations. He'd been quite prepared to accept the dirt dished by the left over his support for the Iraq war but now he found himself being attacked by those who had always constituted his principal reference group: liberal academic human rights practitioners. He was in danger of losing that which he had once loved. What better emotional defence against such a loss than the realisation that these former friends and colleagues published falsehoods, lacked "editorial due diligence", and were incapable of understanding rational argument? Who would want to associate any longer with such a tarnished coterie? Time for Prince Hal to shrug off such flawed associates and prepare for office in Canada.

There is one other possible explanation for Ignatieff's swingeing attack upon Index and all its works. For years he managed to present himself as an apostle of universal liberalism. His record in this respect earned him some tolerance when he frist came out in support of the second Iraq war. But even this tolerance started to wear thin when he embarked upon a series of articles for the New York Times Magazine which were even more stridently pro-war and pro-Bush. On 2 May 2004, he could be found in those pages arguing for new forms of coercive interrogation. "Permissible duress might include forms of sleep deprivation that do not result in lasting harm to mental health or physical health, together with disinformation and disorientation (like keeping prisoners in hoods) that would produce stress." It was unfortunate, to say the least, that this article was already printed and on its way to the distributors when the first pictures came through from Abu Ghraib prison, one of which showed a hooded Iraqi standing on a box.

America's historic role was now defined, with reference to Jefferson, as bringing democracy and freedom to the world and anyone who refused to go along with that project could be written off as back-sliders. "The French used to talk about exporting Liberté, Egalité and Fraternité, but nowadays they don't seem to mind standing by and watching Iraqi democrats struggling to keep chaos and anarchy at bay."

All this might have been meat and drink to the neo-conservatives and military officers with whom Ignatieff enjoyed conversations at Harvard. But it was a step too far for his former human rights colleagues. Ignatieff was no longer merely a supporter of a war to get rid of the tyrant Saddam; he was now an active proselytiser on behalf of all American interventionism. The new US empire's "grace notes", he declared "are free markets, human rights and democracy, enforced by the most awesome military power the world has ever known". His outraged response to the Index article was perhaps an acknowledgement that he could no longer keep his former colleagues on board. The circle could no longer be squared.

Meanwhile, the editors are still waiting for Ignatieff to respond to their renewed request for a written response to Gearty. So far, there is only silence.