When the universal credit computer says no, fragile lives can quickly crumble.

Lucy Morris, a 32-year-old mother of one in Rochdale, was scraping by on her beauty therapist’s wage topped up with UC when she failed to check a box on the benefit’s online form and lost a £400 payment. It was enough to torpedo her finances and before long the heating was off, vegetables were dropped from meals and the house grew filthy because she could not afford cleaning products.

“It is designed to make it difficult so that they can get as many people off it as they can,” she said.

Lucy Morris failed to check a box on the universal credit online form and lost a £400 payment. Photograph: Christopher Thomond/The Guardian

Mark Abraham, a married father of twins in south London, was denied a month’s benefits because an automated system linking salary data from HMRC with the Department for Work and Pensions misreported his previous income from a TV production job. He showed wage slips that proved the pay was reported wrong, but jobcentre staff could do nothing. Food ran low, he broke down mentally and ended up homeless and estranged from his family.

“The DWP staff appeared to be in thrall to the UC computer, allowing it to make all the decisions,” he said. “Being able to tackle the computer beast that had made this decision wasn’t within their capability.”

Mary Blyde, a 61-year-old with incontinence and learning disability, was discovered by a charity worker lying in her unheated home in Gateshead on a urine-soaked sofa after her benefit was cut. She had missed a note on her online account warning her she needed to take action. When a charity worker found her, all that was left in her cupboard were three potatoes, a can of meat and a carton of orange juice.

“Sometimes I get scared the money won’t come into my bank,” she said.

These are some of the lives that campaigners warn risk being forgotten as the government and its technology industry partners pour millions into automation, artificial intelligence and machine learning in the benefits system.

The strategy might seem inevitable, welcome even, given its spread to other walks of life. How we use transport, watch TV and use email are all increasingly shaped by AI. Many UC claimants welcome the ability to communicate digitally rather than waiting on hold on the phone. Ministers argue digitisation will make claiming benefits more straightforward, reduce fraud and save money.

The DWP’s last annual report claimed investment in digital technology “improved the experiences of people who rely on our services, making us more effective and efficient, and enabling us to personalise delivery for customers and claimants”.

The ministry tries to create an atmosphere that will attract programmers to develop technologies for a welfare system that is used by 20 million people. There is an “innovation dojo” to investigate new technologies, and its “intelligent automation garage” – an echo of Google’s Digital Garage training centres which began in sunny California – is looking for ways to leverage the “DWP data lake” for “improved citizen outcomes”, albeit based in a grey government building in north Newcastle.

But many see the reforms as erecting digital walls around the welfare state which are now only scalable by the computer literate. A further digital transformation with robotic automation and machine learning will only make things worse, they fear.

Mark Abraham was denied a month’s benefits because an automated system linking salary data from HMRC with the DWP misreported his previous income. Photograph: David Levene/The Guardian

“It’s massive,” said Shona Alexander, chief executive of Citizens Advice in Newcastle which helps people navigate the system. “They think it’s going to save money but we don’t think it will. The waste from the mistakes is many times more [than the savings]. We are seeing more and more people because they have tried online and can’t do it.”

She recalled a released prisoner who dropped in recently for help signing on for UC, could not cope with the system and said he wanted to go back inside. “He kicked off, the police came and he was arrested,” she said.

Charities are trying to help. Blyde, for example, relies on Gary Fawcett at the Your Voice Counts in Gateshead. He has spent 155 hours on her case, remarking: “It almost broke our project.”

A recent exchange on her online journal was telling. She had already lost almost £1,000 in benefits because she did not know she needed to input more data, so he asked the DWP to tell her about future problems by post.

“Mary CANNOT read or access her journal in any way,” he wrote on her journal. “I can no longer be sorting this out for her.”

The reply came: “We do not communicate by letter … this is an online service.”

Fawcett said again she could not access, read or input into the journal. He asked: “Who is supposed to do this?”

The DWP replied simply that the online system needed updating, signing off: “Please do this ASAP.”

Fawcett is also trying to help Julian Jennings, 65, who cannot read or write, has learning disabilities and does not even know he is on UC.

Julian Jennings: ‘I used to go to the dole. It was much easier.’ Photograph: Christopher Thomond/The Guardian

“I have never used a computer in my life,” he said as he sat at Fawcett’s desk with his UC account screen open. “I used to go to the dole. It was much easier. You talked about it and signed it. If there were any problems they used to sort it.”

There is a message from a UC official: “Hello Julian. Please read the attached letter.”

“I can’t read none of that,” he said, peering at the screen. “How are you supposed to get your money?”

Blyde and Jennings are among 1.5 million people in the UK with learning disabilities and are not alone in struggling with the system. Tears filled the eyes of Danny Brice, 47, in London when he showed the Guardian how difficult he has found negotiating the UC programme with learning disabilities and dyslexia.

“I call it the black hole,” he said. “I feel shaky. I get stressed about it. This is the worst system in my lifetime. They assess you as a number not a person. Talking is the way forward, not a bloody computer. I feel like the computer is controlling me instead of a person. It’s terrifying.”

Nine million people in the UK are functionally illiterate and 5 million adults have either never used the internet or last used it more than three months ago.

And yet many of these people rely on a “digital by default” welfare system.

The DWP said that humans remain available to help: “We continue to invest in frontline colleagues, from phone lines to work coaches to front of house staff,” said a spokesperson. “This means people who struggle with digital services, or are worried about a wrong decision, can get the help they need. And because we know that, for whatever reason, some people don’t want to come into a jobcentre, we are funding Citizens Advice to help support people with their claims.”

Nathalie Nasor at Oasis Community Housing has been helping a client with mysterious benefits cuts which seem to be the result of the system combining different databases. Photograph: Christopher Thomond/The Guardian

Nathalie Nasor, a crisis case worker at Oasis Community Housing in Gateshead, has been helping Gary Warburton, 56, a former industrial cleaner who has been on UC since 2017. They have struggled with mysterious cuts to his benefits which seem to be the result of the system combining different databases.

He recently lost sums which turned out to be repayments for a crisis loan which dated back to 1997, an overpayment of tax credit five years ago, magistrates court fines and council tax arrears.

“It drives you absolutely cuckoo,” he said. “These are things from 1998. They control you and don’t give a hoot what happens to you.”

“His anxiety and mood went to an all-time low,” said Nasor.

The digital system has been very good for fraudsters. Staff have already made 42,000 referrals for fraud, the government has said. Kasim Mahmood, 29, a supermarket worker with Asperger’s in Manchester, was one victim.

Kasim Mahmood, who was defrauded by someone via Snapchat. Photograph: Christopher Thomond/The Guardian

In July he was approached on Snapchat by someone offering him extra cash. As asked, he provided his address, national insurance number and driving licence, and £1,525.44 landed in his account. The fraudster had applied for a UC advance payment – essentially a loan – and it had arrived fast. He threatened Kasim with violence if he did not send half. So now Mahmood was in debt and his existing benefits were stopped because the DWP computer thought he was receiving universal credit.

“I would struggle to get any benefit, yet there are people out there who get it at the click of a finger as long as they know their way around the digital system,” said his mother, Rucksana Mahmood. “There are some things we have to move forward digitally and others keep in the old fashioned way.”

Last year the UN rapporteur on extreme poverty, Philip Alston, warned that the postwar British welfare state was disappearing “behind a webpage and an algorithm” and that the impact on the human rights of the most vulnerable would be “immense”. The then chancellor Philip Hammond said his report was “nonsense”. Later this week Alston will deliver a separate report on the global rise of digital welfare to the UN general assembly in New York.