An NHS hospital where dozens of people suffered impaired vision, pain and discomfort after undergoing eye operations provided by a private healthcare company has been criticised for refusing to publish its report into the crisis.

Patients affected and their families, including that of an 84-year-old man who claimed to have lost his sight following one of the routine cataract procedures, have demanded a full independent inquiry into what went wrong.

Instead Musgrove Park hospital in Taunton carried out its own investigation. It is saying it has found “no clear single cause for the range of problems” of patients – but is refusing to publish the report on legal advice.

A spokeswoman for the Somerset hospital said it had planned to publish the report – and still wanted to do so – but lawyers had advised that “individuals and parties” might sue for defamation.

The decision has caused deep concern among health campaigners and lawyers who are working with some of the patients. It seems to fly in the face of the government’s commitment to openness about mistakes following the Mid Staffs hospital scandal and raises worrying questions about how open health professionals can be when a private healthcare company and an NHS trust work together.

Clara Eaglen, eye health manager at the Royal National Institute of Blind People, said: “We are calling on Musgrove Park hospital to release this report to the public to ensure transparency and openness.

“It is unacceptable that an operation with such low risk of serious complications has left these patients with a reduced quality of life. We think it is very important that the details of what went wrong, and what steps were taken to protect patients, are made public.”

Musgrove appointed Vanguard Healthcare Solutions Ltd in May to carry out 400 cataract operations to help reduce a waiting list backlog of patients needing treatment. The procedures took place in a mobile operating theatre at the hospital site. But half of the first 60 patients, many of them elderly and frail, suffered complications including blurred vision, pain and swelling, and the contract was cancelled. The hospital said at the time it would carry out an inquiry and learn from what had happened.

Musgrove, which is part of Taunton and Somerset NHS Foundation Trust, has revealed that it has finished the inquiry and has shared the findings with patients and would talk to healthcare bodies such as the Care Quality Commission about them. But it said it would not let the general public know what was in the report.

In a statement the hospital said: “We have now concluded a thorough investigation. The purpose of this was to try and establish what happened to cause the complications that the patients operated on in the Vanguard mobile theatre experienced, and how we could learn from these events to minimise the risk of recurrence in the future.

“As with similar ophthalmic incident clusters there is no clear single cause for the range of problems our patients appear to have experienced.

Instead we have identified a number of factors which may have led to the unusually high level of complications seen. The detail of the investigation has been shared with patients.

“We have identified a number of learning points from this incident, many of which have already been implemented as a result of the investigation and others which will be implemented over time. Our intention is to also share our learning across the healthcare community so that the incident can be reflected on more widely.”

Laurence Vick, a medical negligence lawyer who has been approached by some of the victims, said the hospital appeared to be playing down the severity of what went wrong.

He said: “These patients have suffered very real problems, including one of our clients, an 84-year-old man, who has been left blind and requiring a retinal transplant. We have been waiting for this investigation for five months, and it is imperative that it is released to the public.”

Vick, head of clinical negligence at Michelmores Solicitors, said the hospital should share details such as how the private provider was vetted and monitored and whether there was adequate liaison between the NHS staff and Vanguard’s operatives. He said patients and the public had a right to know if steps were taken as swiftly as possibly to halt the contract.

Vick added: “The fear is that, when the private sector is involved, there can be an absence of the transparency that has become a reassuring feature of the NHS.

“There is concern as to whether the NHS should outsource to a private health sector that is still inadequately regulated. Private companies, after all, have a duty to shareholders as well as patients. If they are keen to work with the NHS, they need to be entirely transparent.

“There have long been concerns as to why cataract surgery, which can have such drastic consequences for patients if consequences occur, is regarded as a suitable procedure for outsourcing.

“From the taxpayer’s point of view, we also need to know that Musgrove secured an effective indemnity from Vanguard or its insurers, to cover the cost of compensation claims.”

Ian Gillespie, Vanguard’s chief executive, said: “Our focus remains first and foremost on the patients and their care, and I’d like to personally convey my sympathy for any patients who have experienced discomfort or distress.

“This was a collaborative contract, and we have been working closely with the trust throughout this investigation. The investigation does not identify any one cause, but instead points to a number of different factors which may have led to the complications experienced by patients. No issues have been identified with the Vanguard mobile theatre facility itself; however, there are clearly lessons to be learned by all parties. We are working with the trust to ensure that measures are put in place to prevent this happening again.”