Politicians may deal in terminological inexactitudes, but I can’t think of many black-is-white, war-is-peace practitioners as downright deceptive as Iain Duncan Smith. Originally, the question was whether to put it down to simple stupidity, as he didn’t understand that the numbers he promised were impossible. Yesterday, poring over his big speech on welfare reform, a few of the more polite experts spoke of his “magical thinking”. But his motives and state of mind hardly matter to the millions affected by his evidence-free, faith-based policy-making.

His speech was a paean of self-praise. To read it, no minister has done such good for so many. This was a sublime response to a battery of critics who include Treasury briefers, the National Audit Office on the failure of his work programme, the chair of the UK Statistics Authority for his abuse of figures, and the Major Projects Authority awarding his universal credit an amber/red warning.

The man does have indefatigable self-confidence: “We are fixing society,” he says. The Times, Sun, Mail and Telegraph happily swallowed it whole, rather than explore the thickets of his benefit system. His great claim is that his reforms have been the key driver in getting people back to work.

Let’s start with where he’s right: this recession has been unlike any other, as employment fell by far less and now grows by far more than economists can explain. Fraser Nelson, the Spectator editor, eagerly backed the view that IDS’s big stick has been the “game-changer”.

But Jonathan Portes, head of the National Institute of Economic and Social Research, formerly Treasury and a Department for Work and Pensions economist, makes mincemeat of the claim. Comparing numbers with charts over time, he concludes: “The idea that those on JSA are getting a job more quickly than before the recession, let alone that welfare reform has anything to do with it, has no support in the data.” When it comes to the sick on employment and support allowance, numbers fell steadily from 2004, rose a bit in the recession and were starting to fall on trend. But now they’re rising again. Why? Portes says it’s “the result of the administrative chaos surrounding the Atos contract for the work capability assessment”.

Duncan Smith takes credit for one of Labour’s successes: Labour raised the number of single mothers into work from 46% to 58%. He says it’s higher than ever now, which is true – but only up by 2 percentage points in his time. He hurls accusations at Labour’s welfare bill: welfare expert Declan Gaffney says Labour cut the bill and kept it stable as a proportion of GDP – until the crash. It peaked in 2012 on IDS’s watch.

His universal credit was due this April to cover a million people: so far it covers just 16,000 easy households with no children, writing off £41.1m in failed IT with a further £91m spent on assets “that will support only a limited service for five years with clear consequences for public value” according to the all-party work and pensions select committee. But you would never guess when IDS says it “completes the cultural shift”. Rolling many benefits into one doesn’t magically simplify them: the online form, 50 pages long, still needs to record every changing detail of every member of the household in real time.

Better incentives? Donald Hirsch, economist for the Joseph Rowntree Foundation, finds that on universal credit, families who work full-time can easily end up with less than if they worked part-time. Worse, it traps mothers at home: if one partner works, the second gains virtually nothing by taking a job. Nor does Duncan Smith say that 65p is cut from every extra pound earned. Raising income tax thresholds for the low-paid hardly applies to those on universal credit: most of the gain is lost as their benefit is cut back.

There are traps, hazards both moral and practical, in any benefit system. These deserve debate – but IDS prefers falsifications of reality. The bedroom tax, he says, is imperative. He doesn’t say that only 4% or 5% of people have moved as a result, the rest taking a huge hit, sending them to loan sharks and food banks. Nor does he tell of the doubling, by next year, of the number of working people drawing housing benefit, due to soaring rents and falling pay.

Take the disaster of his 20% cut and transfer of disability living allowance into personal independence payment (PIP). Forced to delay existing cases to after the election, that’s a nasty gift of 1.75 million assessments for his successor. But worse, people applying now are held in a long backlog, often very sick.

Macmillan Cancer Support, campaigning hard about waits of over six months for be

nefits rulings, mentions one typical case: a 25-year-old father with advanced cancer waiting for PIP has almost no money. His wife has had to work while he cares for their baby. Without his PIP, he waits for carer’s allowance, severe disability premium, escape from the bedroom tax, bus pass, taxi cards to get to hospital and heating grant. Latest figures show only 24% of claims have been processed; the rest wait, and some claimants die waiting.

“There is a lot of misleading talk about sanctions,” Duncan Smith says. Indeed there is, by him. Any benefit system has to prevent fraud or idleness, but he must know how his Jobcentre Plus offices have become sanction factories, his staff under unbearable pressure to cut people off. Research by Inclusion finds an unprecedented gap between the number of unemployed and those drawing JSA – invisible people living on thin air.

Last week the Guardian reported the tragic death of a diabetic former soldier, sanctioned into starvation. Go to any food bank and you’ll find heartbreaking cases. Every week, my inbox tells of people struck off unjustly – the latest, Jim, was sent on a course by the jobcentre then struck off for not signing on, as if he could be in two places at once. Tricks abound as staff are forced to hit targets called “spinning plates”. With George Osborne taking another £12bn cuts after 2015, it’s possible Duncan Smith doesn’t know the abominations he oversees.

• This article was amended on 18 August 2014. An earlier version stated that the implementation of universal credit had resulted in “writing off £130m in failed IT”. This has been corrected. In addition the article stated there is a “nasty gift of 3.6 million assessments for his successor” in relation to the numbers of people currently on disability living allowances being transferred to personal independence payments (PIPs). In fact the figure is 1.75m.