It's a bold play for Iain Duncan Smith to reference F Scott Fitzgerald in the course of his tedious, risible political thriller, The Devil's Tune. A female character approaches a grandiose house: “Laura was reminded almost instantly of The Great Gatsby. She smiled at the absurdity […]” (Anyone who’s battled through this shockingly bad novel will feel the absurdity if not the smile.)

A bold play, but perhaps not a wholly inappropriate one, since at least one of Duncan Smith’s barely distinguishable characters owes a debt to Gatsby himself. Democratic presidential pretender Kelp is the epitome of the American dream, according to the novel – an ex-military man who has made his own myth and risen from dirt, with the help of some dubious money and connections. He's also a deeply crooked politician.

Iain Duncan Smith has his myths too. He's the “quiet man”, the man who had the “Easterhouse epiphany”, a man whose compassion for the poor drove him to found the Centre for Social Justice, where his honest intentions become honest research. He'd like it to be believed that he – like Gatsby – has hauled himself up from common stock, but that's not quite true. Nor are many of the other things that are widely believed about him, but he is like Gatsby in one regard: he's a great work of self-fictionalising. The end result, sadly, is no match for the luminous Mr Jay. Let us think of IDS instead as the Great Crapsby.

The narrative of the Great Crapsby is one of fall followed by resurrection, hinging on a single dramatic incident of enlightenment. Following his unlikely victory, Duncan Smith was a humiliation as Conservative party leader, his reign of just over two years was marked by embarrassment and ineffectiveness. His pitiful parliamentary performance won him the name “Iain Duncan Cough” in Private Eye, and having once betrayed Major, Duncan Smith reaped the disloyalty of his party in turn.

After he was deposed in 2003, it seemed plausible that he would vanish into the political scrub. Instead, he founded the Centre for Social Justice – the allegedly independent think tank that would do so much to promote and shape Conservative policies on welfare and society, and that established Duncan Smith’s credentials to take on the work and pensions portfolio.

Stories of the CSJ’s origins routinely mention something called the Easterhouse epiphany. “It was on the Easterhouse Estate in Glasgow where I began to appreciate the scale of social breakdown occurring in Great Britain,” writes Duncan Smith in one of the Centre’s publications; “The CSJ was born through a visit to Easterhouse Estate in Glasgow,” he says in another. In 2010, Tim Montgomerie described the Easterhouse visit as the moment “something suddenly clicked […] he realised here was his personal mission and a mission for the Tory party.”

So far, so Damascene. (And it’s worth remembering that the apparatus of piety plays a large part in the iconography of IDS – he has claimed that “My Catholic background […] has become integral to everything I do.”) But – besides people saying that it happened – what evidence is there for this miraculous moment of enlightenment? Not, it turns out, very much at all.

In 1994, Duncan Smith (then working in the Department of Social Security, predecessor to the Department of Work and Pensions) wrote an editorial for the Mail (the text of which is copied here). In it, he decried the growth of spending on welfare since the foundation of the welfare state; he claimed that the benefits system had betrayed the intentions of the Beveridge Report, and was being defrauded and abused on a vast scale. Worst of all, he alleged, the welfare state had created a class incapable of self-help: “[T]he system discourages people from getting a job […] people become trapped, remaining dependent on the State rather than on their working abilities.” His answer? “There should be just one, income-assessed benefit.”

In 2010, Duncan Smith (now work and pensions secretary) delivered a speech. In it, he claimed the benefits system had betrayed the intentions of the Beveridge Report, that it was being defrauded and abused on a vast scale, and worst of all, that it was counterproductively “supporting – even reinforcing – dysfunctional behaviour.” His answer? Universal credit.

Over 16 years, there was only one appreciable difference in the rhetoric: in 1994, Duncan Smith claimed that it was particularly appalling to see welfare spending expand during a time of economic growth; by 2010, the argument for urgent action was that “the economy isn’t growing as we had hoped”. But that change is simply a matter of shaping the argument to the political conditions. Whatever Iain Duncan Smith discovered in Easterhouse in 2002, it did nothing whatsoever to alter his politics. His diagnosis and prescription for the welfare state has remained constant, from the Nineties to now. The “epiphany” is a useful fiction, nothing more.

It feels painful to impugn Duncan Smith’s honour like this, because the perception of him as a decent man is so strong, even among those who oppose his politics. In some ways, his ineptness as a party leader has come to be seen as evidence of his virtue: his failure as a politician is proof of his good faith. But a certain taste for self-fashioning has long been evident in him. In 2002, Michael Crick discovered what might kindly be called exaggerations in Duncan Smith’s CV. It stated that he had attended the Universita di Perugia. This was not true: instead he had been to a language school in Perugia, and had not received any qualifications. Duncan Smith is a Perugia man in precisely the same way that grifting Gatsby was "an Oxford man".

When he isn’t bloating his qualifications, Duncan Smith can be found putting on the poor mouth and talking up his experience of poverty. Having haplessly claimed that he could survive on £53 a week “if I had to”, Duncan Smith was forced to plead personal experience. After he left the army, he told the Mail, he lived illegally with his then-girlfriend, now-wife Betsy Freemantle, in a ragged bedsit. “They say love makes everything work,” said Duncan Smith, although presumably the fact that his partner is the daughter of a monied aristocrat and the recipient of an inheritance in her own right also went some way to making everything work. Whatever privations the Duncan Smiths may have experienced, there was always the comforting hand of wealth to keep them from plunging into the underclass. They now live – rent-free – in the Freemantle ancestral home.

So he may not know directly what it is to be truly poor, his defenders can say, but at least he has studied the issue through the Centre for Social Justice. Well, that depends on what it means to study something. The CSJ has published report on report, all of them with the curious effect of reinforcing its founder’s prior positions and supporting government policy. (The intimacy of the CSJ and DWP is underlined by the fact that, until late 2012, Philippa Stroud was both a special advisor to Duncan Smith at the DWP and paid by the CSJ to be co-chair of its board of advisers.) Few of us have the divine inspiration that lets our hypotheses precisely anticipate the results of our research, but Duncan Smith appears to be one of those saintly, second-sighted few.

Either that, or he has no respect at all for evidence. In 2010, Duncan Smith made a number of claims about the stymied brain development of children who “witness a lot of abuse", or whose mothers have "different, multiple partners", citing the work of Dr Bruce Perry. Perry protested that his work had been “distorted”: while Duncan Smith implied that children of chaotic or neglectful households were destined to criminality, Perry’s work had in fact been on children who suffered extreme deprivation, including being locked in a basement without human contact. Yet Duncan Smith maintained, implausibly, that he not misrepresented Perry’s findings.

This wasn’t an isolated case of over-enthusiasm. Here’s another: in April, Duncan Smith claimed success for the benefits cap before it had even been implemented, saying: “Already we’ve seen 8,000 people who would have been affected by the cap move into jobs. This clearly demonstrates that the cap is having the desired impact.” Again, the original research showed nothing of the sort. On 9 May, Andrew Dilnot of the UK Statistics Authority wrote: “[the statement] is unsupported by the official statistics.” Furthermore, Dilnot’s letter to the DWP points out there have been previous incidents of statistical abuse in the department, and requests “further assurance that the working arrangements within the department give sufficient weight to the professional role and public responsibilities of statisticians.”

It is one thing to be an individual fantasist, telling flattering stories about yourself. It is another to insist that government policy should be directed by fantasy. But the final tragedy of the Great Crapsby is that, for all the dull power of his imagination, reality stubbornly refuses to comply. The work programme, which Duncan Smith launched two years ago, doesn’t work. The hardest cases are neglected while private providers profit from shuffling the easily employable into jobs.

Universal credit – the single benefit that Duncan Smith has been arguing for since the 1990s – seems unlikely to happen in this parliament, after widely predicted problems with the computer system saw the trial reduced to a minute population that included only individuals with the simplest circumstances. In the Cabinet Office’s Major Projects Authority review, universal credit was given an amber/red status, meaning “in danger of failing”.

The Great Gatsby had his vast wealth and a belief in the green light. The Great Crapsby has his vast wealth and an irresistible attraction to that red light of failure – not just his own personal screw-ups, but a belief that the poor must be made to fail and ground down as far as possible. How we must hunger for saints in our politics if we accept a man as good purely because he says he is good, while so much of what he does bespeaks falsehood and a perfect absence of empathy.