Ministers have been accused of a cover-up for refusing to release official reports into whether migrants’ health has been harmed since they began being charged upfront for NHS care before they can be treated.

The leaders of Britain’s doctors, nurses and midwives are demanding the release of three government reviews into how hostile environment immigration policies have affected access to NHS care.

In 2017, the Department of Health and Social Care (DHSC) commissioned three separate investigations into key aspects of its decision to compel NHS trusts in England to implement upfront charging from October that year.

It published a summary of its findings late last year. However, it has still not published the reports themselves, despite growing evidence that very ill migrants, particularly people who have been refused asylum or overstayed their visas, have wrongly been denied vital treatment for cancer, heart disease and pregnancy.

The DHSC has resisted attempts by MPs and campaigners to gain sight of the findings using parliamentary questions and freedom of information requests.

Medical bodies, MPs, health unions and organisations that help migrants have written a joint letter to the health secretary, Matt Hancock, voicing frustration at the continued stonewalling. Signatories include the royal colleges representing GPs, nurses and midwives, public health specialists, six Labour and Green MPs and MEPs, the NHS campaign group Docs Not Cops and others.

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In submissions to the reviews, the health charity Doctors of the World and other groups that work with migrants showed that advance charges were leading to sick people missing out on healthcare because the rules were being applied too harshly.

“We would have expected the government to have taken this evidence seriously and been transparent about the impact the policy was having on patients.

“The decision not to publish the findings of these evaluations makes us concerned about what is being covered up”, said Lucy Jones, the director of programmes at Doctors of the World.

The National Aids Trust said the DHSC had “buried” the reviews.

Yusef Azad, its director of strategy, said: “The government is always asking health professionals to provide evidence of the harms of NHS migrant charging and data-sharing practices. Yet when we do – and there is a lot of evidence – the findings are buried.”

Upfront charging was introduced as part of the government’s hostile environment approach to immigration developed while Theresa May was the home secretary from 2010-16.

The Guardian has highlighted several cases in which NHS trusts broke the rules governing upfront charging by refusing to treat individuals who were eligible, some of whom later died. Many involved hospitals misapplying the rule that states that anyone needing “urgent or immediately necessary” treatment should get it as soon as possible, irrespective of their immigration status.

In the letter the co-authors outline their “serious concerns about the lack of transparent evaluation of NHS migrant charging and data-sharing policies, and request a full and independent review of these policies and their impact on individual and public health.” They also urge Hancock to immediately suspend the charging regime until the amount of harm it is causing can be established.

“Much greater transparency is needed. The decision not to publish the findings of these pieces of evaluation work risks damaging trust in the DHSC and partnering agencies, and their commitments to be open and transparent”, the letter adds.

Under the upfront charging system, access to GP and A&E care is free but those deemed ineligible have to pay for most forms of hospital care, such as chemotherapy and treatment of heart conditions. But migrants’ rights groups claim many vulnerable migrants have been put off accessing any form of NHS care because they are scared that they will have to pay, even when they will not be changed.

The Academy of Medical Royal Colleges, which represents all of the UK’s 240,000 doctors professionally, has also signed the letter.

A DHSC spokesperson said: “We conducted a review on the impact of the 2017 amendments to the NHS charging regulations with evidence submitted by stakeholders, some of it in confidence. All evidence was considered thoroughly before a summary of the findings and steps the department is taking was presented to parliament in December 2018.

“We are working with NHS Improvement to ensure providers are applying the regulations properly and fairly and we continue to keep the impact of the regulations under review, working closely with interested groups to further develop our guidance for patients and healthcare professionals.”