“I think it’s horrible and inhuman to have a person who is sick like me dumped on to the street without food or shelter or medication,” says Esayas Welday. He is as confused as he is angry that it was an NHS trust, not a rogue landlord or uncaring staff of a benefits office, that forced him back into being homeless and did so even though he was suffering from cancer.

The Eritrean asylum seeker was relieved when he began the first of five courses of chemotherapy last May for acute lymphoblastic leukaemia, a form of blood cancer he had just been diagnosed with at the age of 29. But one day several weeks later, without warning, staff at Northwick Park hospital in west London told him he had to leave and that he would not receive any more treatment.

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“They said they couldn’t continue to treat me because I couldn’t afford to pay the £33,000 bill for treatment they had given me. They decided that they didn’t care about my life, or my health and my illness, so they sent me back to the street. I thought they were killing me,” Welday says.

He was sent away with a jumble of medications for his cancer in a plastic bag. His protestations that he had no fridge to keep them in, because he was about to become homeless again, fell on deaf ears.

“I asked them where I was going to go,” he said. “They said they didn’t know. I told them that meant I was going to go back to the street and that I was going to die and that I was now without hope.”

Northwick Park’s justification of its action illustrates the widespread ignorance and confusion among NHS trusts about how to apply regulations which the government forced them to adopt in October 2017 as part of its hostile environment approach to immigration.

The rules compel trusts in England to charge most undocumented migrants, including refused asylum seekers, upfront for many forms of hospital-based medical care, even though such patients, like Welday, are usually penniless and often destitute. That regime, which many NHS staff say is unethical and dangerous, has led to hundreds of people missing out on care for sometimes life-threatening conditions such as cancer, arrhythmia and chest pains.

The trust claimed: “Mr Welday is not eligible for NHS treatment … he is homeless with refugee status.” That was untrue. He had not by that time acquired refugee status.

The joint Council for the Welfare of Immigrants (JCWI), which has helped Welday, said he still should have received NHS care because his treatment was “urgent or immediately necessary”. If he had had refugee status, as the trust believed, then that, too, should have made him eligible for treatment. Either way, he should have completed his chemotherapy, not been discharged.

London North West University Healthcare NHS trust, which runs Northwick Park, denied they withdrew treatment because Welday could not pay and denied he needed urgent treatment.

The trust said in a statement: “We completed a full course of treatment for this gentleman’s condition. It is not true to say that he was discharged from our care because he was unable to pay for his treatment.

“When [our doctors] assess that such treatment is urgent, we continue to offer care regardless of whether someone can pay for it or not. If someone in this position is not eligible for NHS care, they will receive an invoice later, as we are required to do by law.”

Ellen Fotheringham, Welday’s caseworker at the JCWI, said Welday was seriously traumatised by Northwick Park telling him to leave.

“It’s a woeful reflection of the NHS charging regulations and the hostile environment as a whole that a human life was completely disregarded by the NHS, simply because he did not have the right papers, and worse, the decision to disregard his life did not even comply with the law,” Fotheringham said. The JCWI is one of six charities helping people affected by the hostile environment that will benefit from the Guardian and Observer’s Christmas appeal.

Welday was lucky, though. When the father of two became very ill again, he ended up in the A&E unit at the Whittington hospital in north London. Staff there did know the rules and arranged for him to go back to Northwick Park and have the rest of the chemotherapy. After completing that treatment, he is waiting to have a stem cell transplant next week, with a cousin acting as his donor, which he hopes will cure his leukaemia.

His situation has improved. The British Red Cross has found him temporary accommodation and the JCWI has helped him get leave to remain for two and a half years from the Home Office. But he remains bitter about starting potentially life-saving treatment only to have it then taken away.

“I’ve seen both the caring side of the NHS, like the staff at the Whittington, but also the uncaring staff, like the managers at Northwick Park who decided to dump me. I just want the rules to be applied properly so that other people don’t suffer the way I did,” he says.

• This article was amended on 22 January 2019. An earlier version referred to the rules compelling trusts “to charge refugees and asylum seekers”. This has been changed to the more accurate description of those being charged as “most undocumented migrants, including failed asylum seekers ”. It was further amended on 30 January 2019 to remove an incorrect suggestion that 29 was an unusually early age for the diagnosis of acute lymphoblastic leukaemia.