Thousands of vulnerable people on low incomes – particularly those with mental illness – are at risk of destitution because they do not have the skills or support to apply for and maintain a universal credit benefit claim, the Salvation Army has warned.

The Christian church and charity said there was “overwhelming evidence” that many people found it a struggle to engage with the mainly digital benefit, leaving them unable to pay rent or buy food and effectively locking them out of employment support.

It called on the government to increase the level of support to make it simpler for vulnerable people to make a claim before the next phase of the universal credit programme later this year, when about 750,000 ill and disabled benefit claimants start to be moved on to the benefit.

“Rolling out universal credit in its current form will steamroll vulnerable people into poverty, but the government has time to turn this around by accepting our recommendations and making it easier to apply,” said Rebecca Keating, the Salvation Army’s employment director said.

There is concern among campaigners and even the government’s own social security advisers that the government has not done enough to ensure vulnerable claimants do not fall out of the system altogether when they are transferred to universal credit in the process called managed migration, which is due to start in late autumn.

Claimants with mental health problems, learning disabilities and physical disabilities, as well as homeless people were especially at risk, it said. Some lacked computer skills, or could not access the internet because they did not own a smart phone or because there was no public computer nearby.

The charity cited the case of Daniel, a young man with dyslexia, who struggled to read and write. He had his benefits stopped and ended up homeless after putting the wrong phone number on his online form and missing a text appointment with the job centre.

Although Daniel was allocated a key worker he said the extent of his dyslexia was never fully understood. “I needed things explained to me properly and I couldn’t read all the leaflets he was giving me to go away with. That went on for six months,” he said.

The government’s own figures showed one in five online claims were dropped before they were completed, the Salvation Army said, suggesting 20% of people who were eligible for universal credit because of low pay or unemployment were effectively dropping out of the benefit system.

Some of those who managed to sign up to universal credit subsequently dropped out after being sanctioned for failing to keep up with its tough conditionality requirements, such as 35 hours a week of online job searches. These rules, known as claimant commitments, often did not take a person’s vulnerabilities into account

About 85% of those interviewed reported problems signing up to universal credit. Of those, 42% said mental ill health was a barrier. The charity said that overstretched job centres were failing to identify vulnerable people and offer them appropriate support, while government help to claim programmes could not meet demand.

The charity insisted it wanted universal credit to be a success, but it had a duty to point out where it was going wrong. “This is not just another paper for decision-makers to ignore and label as scaremongering,” it said. “These are people’s lives.

“We are not saying ‘bin universal credit, it’s no good’; this is about us wanting to make the system work,” said Keating. “Digital works for a lot of people but there is a significant group of people that it is not working for.”

The Department for Work and Pensions said that although 98% of people make their claim for universal credit online, people who struggled with computers were able to make a claim in person or over the phone. Extra support was available through the Help to Claim service, delivered by Citizens Advice.

A DWP spokesperson said: “Jobcentres across the UK have staff trained in supporting vulnerable people and tailor people’s benefit claims to match their circumstances, including taking into account mental health, issues with domestic abuse and homelessness.”

The Salvation Army’s research was based on interviews between March and June 2019 with 160 people across England and Wales who were out of work and looking for a job and had signed up to the charity’s Employment Plus programme.