She calls it: "Heartbreaking, truly astonishing, I've never seen anything like this." Emma Cross is a senior Macmillan Cancer Support benefits adviser, and she says delays in Iain Duncan Smith's new personal independence payments (PIP) leave the sick utterly destitute. "Does anyone know how many people are struggling?"

Macmillan's mountain of PIP cases includes a mother being treated with chemotherapy for bowel cancer, whose operation left her with a colostomy bag. She gave up work and, with no other family to help, her husband gave up his job to care for her and their two-year-old child, taking her to frequent hospital appointments. They claimed PIP last September – and they have heard nothing since. No-one answers queries, lost in the gigantic backlog.

Until registered for PIP, which pays from £21-£134 a week, they can't claim other crucial benefits: carers allowance, severe disability premium, escape from the bedroom tax, a bus pass, taxi cards to get to hospital, or a heating grant (she feels intensely cold). With credit cards maxed out, they have no idea what they're due as PIP has tougher criteria: if this woman can just about walk more than 20 metres, she may get nothing now for mobility. Macmillan says people in this backlog are missing chemo appointments for lack of a bus fare.

"I wish this couple were an exception," says Emma Cross. "But this is happening to so many."

PIP replaces the disability living allowance, which Duncan Smith cut by 20% and abolished for new claimants; old claimants are being moved over. It used to pay out quickly, but PIP is an administrative calamity. The public accounts committee (PAC) queried why Atos won the contract to run it with its record of failure: Sue Marsh's latest Spartacus report says 43% of appeals against DWP decisions based on Atos tests for employment support allowance are upheld. Margaret Hodge, the PAC chair, unearthed Atos's tender for the PIP contract and found it had been "grossly misleading", pretending to have hundreds of test centres inside hospitals, when in reality it had very few.

The last figures from the Department for Work and Pensions (DWP) show that 220,000 made PIP claims, but less than a fifth were processed. Ask any MP about PIP cases piling up in their surgeries and all parties tell tales of woe.

After he appeared on the Andrew Marr show this week, I challenged Duncan Smith over the PIP backlog. He waved it away airily. Oh, it'll all be sorted by the autumn, he claimed. Nothing to worry about. That's highly unlikely – but if so, why not pay claimants the old DLA until it's fixed? Why should sick people pay the price for his maladministration? He batted away the idea with a shrug.

This is exceptionally monstrous, as Macmillan say people have died waiting. The 5% of cases dealt with as priority under "special rules" are those with a doctor's letter certifying they'll die within six months. Macmillan says it's hard to know when people will die – six months or two years. Doctors rightly can't write such a letter for someone who hasn't asked for a specific death date. People need the money right now, regardless of the ghoulish prognosis demanded by DWP.

Labour's Rachel Reeves and her team have been protesting, but the PIP story hasn't become a national scandal. Why not? They say, glumly, that only the Mirror and the Guardian are interested, the rest turn away. Google PIP and you get myriad stories on breast implants. This reflects how much more tribal the rightwing press has become. The Guardian, as did I, covered Labour's failings in power. The PIP saga is a "good" story. Where – yet again – is BBC news, which should be following the DWP with laser-accurate analysis?

Forget civil service factual information: Duncan Smith has just hired a Murdoch managing editor from the Sun and Sunday Times as DWP communications director. Perhaps he helps hone Duncan Smith's terminological inexactitudes [see footnote].

On Sunday's programme IDS claimed, again, that his bedroom tax simply followed Labour's rules on restricting the number of bedrooms claimable on housing benefit in the private sector. Not so, says the House of Commons library, it was the Tories in 1989 who cut the number of eligible bedrooms – and only for new rentals, never turfing people out of homes they already occupied.

The PIP catastrophe is just the most extreme of Duncan Smith's disasters. Nothing – not one of his programmes – has worked as planned. It hardly matters that universal credit (UC) is years late, but last month the PAC demonstrated UC will never do what Duncan Smith claims, its work incentives shot to pieces. With council tax, housing benefit cuts and national insurance, many on UC will lose almost all of every extra pound earned, while most lose 65p or more. The very rich down tools over a loss of 50p in the pound. At first, it might have been ignorance, but now IDS knows his claims for UC are untrue.

After IDS's most recent interview on the Today programme with Evan Davis, the Child Poverty Action Group analysed his facts. Will he meet his child poverty targets? "I believe we will", Duncan Smith replies. "But you're not on target to do that." "I believe we will." "So frustrating!" exclaims Davis. Duncan Smith makes this claim: "Since I've been in power we've seen child poverty fall by 300,000." He knows that's just from the first year when Labour's increase in child tax credits kicked in: since then, it's all downhill.

Duncan Smith likes to mislead on the relative measure of poverty: "Actually upper incomes fell, so the idea of a relative income measure doesn't make any sense." But relative poverty has nothing to do with what happens to top incomes. It's measured against the median – the middle point, not an average nor the top. Stupidity or duplicity? Take your choice.

"The last Labour government spent £175bn in tax credits chasing a poverty target they failed to meet," he said. But that was over 11 years and it did hit two-thirds of the target, while IDS plunges ever downwards.

If your eyes glazed over, that's what he counts on. Bamboozling voters who don't have graphs to hand is how he gets away with it. When challenged, he resorts to "I believe I'm right". But the Institute for Fiscal Studies, Royal Statistical Society and scores of experts stopped him moving his goalposts. The IFS predicts he'll put 300,000 more children into poverty by next year, up nearly a million by 2020. In 2011 IDS claimed his was "the party of the poor" – that's a promise he has kept. Of all his calamities, PIP is probably the worst.

• Comments on this article will be launched later this morning (UK time)

• This article was amended on 11 April 2014. The earlier version said incorrectly that "Atos, the firm contracted to deliver it [PIP], has walked away". Atos's contract to deliver PIP is to continue as planned; it is Atos's separate contract to administer work capability assessments (WCAs), used to determine qualification for employment and support allowance, from which the company has announced it will be exiting early. The article also referred to "appeals against Atos tests". To clarify: the appeals are against DWP decisions based on WCAs.

• The following correction was published on 15 April 2014: A Comment article about the treatment of disabled people by the Department for Work and Pensions (DWP) stated: "Forget civil service factual information: Duncan Smith has just hired a Murdoch managing editor from the Sun and Sunday Times as DWP communications director. Perhaps he helps hone Duncan Smith's terminological inexactitudes." We are happy to accept that Richard Caseby, the strategic director of communications at the DWP, carries out his duties in a thoroughly honest, diligent and professional manner. He was not hired by Iain Duncan Smith, the secretary of state for work and pensions, but works as a civil servant. We apologise for any misunderstanding. In addition, the writer of the article said that "PIP replaces the disability living allowance" (DLA). To clarify: DLA is still available for children up to the age of 16.