Protests against the bedroom tax will spring up on Saturday in at least 60 towns and cities, through a crowd-sourcing of local groups shocked by what's about to happen. Some organisers are from Labour parties – with Liam Byrne, the shadows work and pensions secretary, speaking at one in Birmingham – unions, the SNP and Plaid Cymru – but many have been spontaneously assembled, mostly by women, as people wake up to unfolding local tragedies.

With just two weeks before the arrival of a tumbril of cuts rumbling towards low-earning households, people are only now receiving letters warning what to expect. Any remaining advice services are being flooded with anxious tenants. As I listened in with the NextDoor Project, a homeless charity, almost everyone who came in was expecting to be evicted and sent far away. One distraught woman who is paid a carer's allowance for looking after her severely mentally ill brother (along with her own three children), said she would have to leave him to social services: his room would now be counted as "spare" because a brother doesn't count as family. Perverse and expensive consequences are erupting everywhere, with Labour MPs rarely, if ever, encountering such a tsunami of heart-rending cases.

Many of the government's welfare "reforms" are unravelling loudly in one way or another, though some cause silent suffering behind family front doors. According to the Institute for Fiscal Studies, the heaviest and deadliest cuts are the quietest. Like carbon monoxide building up behind a faulty flue, living standards are being slowly asphyxiated by the invisible loss of benefit upratings: the change from the retail to the consumer price index to calculate benefits, the freezes and the 1% cap make the greatest cuts to the Department for Work and Pensions budget, as inflation eats away at benefits.

The cuts that make most noise are those deliberately devised as eyecatching political crowd-pleasers, yet often saving small sums. Exploiting one-off anecdotes about benefit "scroungers" in high-rent Kensington palaces may have worked as a clever cover, but the truth about the imminent bedroom tax is starting to emerge. Well over a third of social housing tenants have a "spare" room and must pay an average £14 a week more – £700 a year – or move out. That's 20% of unemployment pay. The north is harder hit as its social housing, on cheaper land, has more bedrooms: in Hull 4,700 families are "over-occupiers", with only 73 one-bed flats to move to. In Brighton a thousand families are hit, as the council expects to lose £1m in rent arrears.

Lord Bassam, Labour's chief whip, is collecting a bursting portfolio of cases to send to Downing Street.

There is a disabled man in Reading, with a chronic lung disease, who writes: "My partner, also my carer, and me share a home but not a bedroom, as most nights I am coughing and vomiting. Obviously this would keep her awake,"

Or the sick father who cares for his severely disabled son three nights a week in a ground-floor flat adapted for his wheelchair, but is told one bedroom is enough.

Or this distressed woman: "My partner has paranoid schizophrenia. The second bedroom is now classed as spare. I wonder if anyone has tried to sleep with someone with this condition, as it is virtually impossible."

The Hartlepool Mail tells of the Bell family whose third child, seven-year-old Becky, died of cancer in January: her bedroom is now spare so they must pay or move. As such cases catch the attention of the press, even people who tell pollsters they regard everyone on benefits as idlers are starting to say, "But I didn't mean people like them."

Nothing about the bedroom tax works. The government estimates that 660,000 households will have to pay up or move, but already these figures look wildly wrong. Lord Bassam's survey of south-eastern councils suggests the true national figure will be more than 900,000 households. With only two weeks to go, ministers are still scrambling to duck the falling masonry. After months of warnings, foster carers were this week exempted, along with the few young solders still living at home. Otherwise, whenever challenged, ministers refer to the puny £30m discretionary housing payments pot, temporary money to ease the worst hardship – but spread among the 230,000 disabled "under-occupiers", few will be helped. Cameron, blustering in the Commons, wrongly claimed that disabled children were exempt.

Who are the "under-occupiers"? Pensioners rattling around in family homes are the great majority – but they're exempt. Social and private tenants have least space, while 49% of owner-occupiers have spare rooms. The government claims the bedroom tax will save £480m. But the only savings would come from already low-earning families refusing to move – and so uproot children from school and themselves from jobs – and taking the £700 hit to their wallets. How perverse and dishonest that savings are only made if people don't move. This is simply another deep cut.

But it's worse than that. If people do move, most will go into private rentals, where, even with one fewer bedroom, rents are far higher – to be picked up by housing benefit again. Whether in Liverpool or London, a one-bed private flat costs far more than two-bedded social housing, so everyone loses in this ideological and vengeful political upheaval of often vulnerable lives. The right may be hard-hearted about mass evictions, but if they were equally hard-headed they'd see this "reform" is a loss-maker.

On one thing the government is right: housing benefit is a gigantic bill. That's because property prices and rents have been allowed to rise without control. Though housing benefit costs have risen less than property prices in recent decades, most of this taxpayers' money flows into landlords' pockets. A few years of rent controls would hold down the bill – and stop a new house price bubble, until a massive housebuilding programme from some future more visionary government tames the market. Until then, turfing families and disabled people out of secure homes and jobs means high extra costs for schools, hospitals and social services, with rising council rent arrears, none of it factored in. George Osborne will be the one pulling down the blinds on a monumentally expensive policy disaster.

Time to join one of the protests near you, listed at the Green Benches website. The worst affected are least likely to be able to stand up for themselves. If it's true many young people are disengaged from social concern for others, then it's time for battalions of the middle-aged with energy and child-free time on their hands to lead protests such as these.