The UK government has found a new way to obtain vulnerable patients' private details without even asking their GP, Buzzfeed News has reported today in an investigative story that uses exclusive evidence and interviews from Doctors of the World.

We totally oppose the government asking NHS Digital, the body that stores patients' data, for people's home addresses and other private information as part of an immigration crackdown. This exploits the confidential relationship between a doctor and their patient.

“This could be the start of a slippery slope - if the NHS is already sharing vulnerable people’s private data with the government, there’s no guarantee this practice will not spread to other patients," says Leigh Daynes, the executive director of Doctors of the World UK. "This is not a niche issue, such a huge erosion of rights affects us all.”

At our UK clinics, we already regularly see people who are too scared to see a doctor in case their private details are shared with the government and used against them. A Filipino woman recently came to our clinic in east London and told us she hadn’t gone to her hospital appointment – even though she needed to be tested for breast cancer.

The UK government has for many years sent requests to NHS data departments when trying to track down undocumented migrants. But previously the government often had to write directly to GPs to request a patient’s address – and these doctors were a potential hurdle when they chose to protect their patient’s privacy and refused to share information.

We received one such letter in 2016 and another NHS GP has shared with us three similar letters that they have received. We refused to hand over patient information, as did the other GP who contacted us.

However, on 24 January the government disclosed that it now asks NHS Digital to share patients’ home addresses. This extension could mean that in many instances that the GP is effectively bypassed and never contacted.

Making people too afraid to see a doctor causes a range of serious problems. When GPs spot and treat problems early, this helps patients in need recover quickly, stops illnesses from spreading, and saves the NHS money further down the line by cutting the need for costly emergency treatment.

“We’ve had to start to tell patients at our clinics that their data is no longer private and some just walk out," says Phil Murwill, who runs Doctors of the World's clinic in east London. "The long-term impacts of this could be huge, including more people dying at home and more women giving birth at home alone, with all the risks that entails.”

The government's latest move is part of a wider aim to create a "hostile environment" for undocumented migrants. In December, a data-sharing deal was also disclosed between the Home Office, the government department responsible for immigration, and the Department of Education. Under the agreement, education officials could share the personal details of up to 1,500 schoolchildren a month, the Guardian has reported.

Kingsley Manning, the former head of NHS Digital, spoke out on BBC Radio 4 last week about the government pressuring him to share patient data despite his objections.

“[The NHS] is a safe haven for your data…except if you’re an immigrant and except if the Home Office wants it," he said.

"There’s no right of appeal, there’s no oversight, and there’s no transparency.”