The family of a man whose death was blamed on negligence at a private London hospital have said they are “horrified” by the decision of a health watchdog to rate the clinic “outstanding”, even as a coroner’s investigation into its conduct and the actions of some of its nursing staff is ongoing.

Robert Entenman was the second man in his 50s to die in an incident involving the negligent use of equipment at London clinics run by HCA Healthcare UK.

The company has been given two months to respond to a “preventing further deaths” report issued by a coroner investigating the unexpected death of Entenman, a 57-year-old father of two.

But last week the Care Quality Commission – the regulator that has come under heavy criticism for failing to notice poor practice in care homes – awarded London Bridge hospital an “outstanding” rating, and admitted its inspectors had been in the centre just weeks before an inquest found that neglect by staff had led to Entenman’s death.

His widow, Athina Entenman, said she was “horrified” by the CQC’s report, pointing out that assistant coroner Henrietta Hill had also raised questions over whether Entenman should have been considered for surgery in the first place.

The inspectors’ report was released in the same week that the coroner sent the “preventing further deaths” report to the hospital, the chief coroner and the Nursing and Midwifery Council.

“We chose a renowned keyhole surgeon to treat my husband, and London Bridge hospital was one of two venues he operated in. This seemed like a good choice because it was near enough for me and our two young children to visit Robert every day,” said Mrs Entenman, who plans to take civil action against the hospital once the coroner’s investigation is complete.

“Robert was a very special man, full of life. Our lives have been forever affected. The children are crushed by his death and miss him badly, every day. Robert’s elderly father had to bury his own child. This should never have happened.”

Entenman, a New Yorker, fell in love with London as a student and came to live in the UK 30 years ago, meeting his wife here in 2003. Described by Mrs Entenman as overweight but strong and rarely ill, he decided to have what should have been a routine valve repair operation following heart palpitations a few years before. He needed it done quickly and chose the private hospital, being told by one of the surgeons that the keyhole surgery was a “walk in the park” with a 99% chance of success, and that test results made him a suitable candidate.

But Entenman suffered from diabetes and weighed 145kg, and in theatre the simple procedure turned into major open-heart surgery lasting 10 hours after the surgeon – who was not criticised by the coroner – encountered “hurdles”, including too much fat around the heart.

It is unbelievable the errors that happened in this case, and the coroner is clearly concerned Paul McNeil, Entenman family lawyer

After the operation, Entenman was sedated and put on a heart and lung ventilator. Mrs Entenman was told he was not in danger. But as he recovered, a nurse switched off a humidifier – a key piece of equipment designed to stop mucus building up in his breathing tubes. Two other nurses failed to notice and for 19 hours the machine remained off. The result was a buildup of secretions in the pipe to his airways. “I think it was most likely that that, in retrospect, was the cause of the arrest,” one doctor told the inquest.

Hill has also indicated that she wants to look at any possible connections with the death of Shaun Fagan, a 50-year-old father of two from London who suffered “catastrophic” brain damage at another HCA Healthcare hospital, in Harley Street. An inquest in 2015 found that nurses had failed to notice his oxygen tube had become dislodged, despite alarms going off for nine minutes.

Janene Madden, chief executive of London Bridge hospital, said: “We extend our deepest sympathies to Mr Entenman’s family. We aim to deliver the highest possible standards of patient care at all times and the wellbeing of patients is always our utmost priority. We are reviewing the recommendations from the coroner to ensure standards of care are continually assessed and improved.” At least one of the nurses involved in Entenman’s care is still working at the hospital.

Paul McNeil, a lawyer from the firm Fieldfisher, representing the Entenman family, said: “This is such a catastrophic case. We say he should never have been put forward for keyhole surgery in the first place. It is unbelievable the errors that happened in this case, and the coroner is clearly concerned at the level of training somewhere where three nurses make the same mistake.

“People think private healthcare means they are getting the very best because they are paying for it. That’s not always necessarily true, and that makes it so important that there is total scrutiny of what happens there.”

The CQC said: “It is always tragic when a patient dies in avoidable circumstances. This happened at the London Bridge hospital in May 2015 and prior to and after the subsequent coroner’s inquest the hospital said it had taken steps to review its policies. CQC’s inspection team was aware of what had previously happened at the hospital.

“CQC inspected the hospital in September 2016 and rated it as outstanding overall. Inspectors noted that in relation to the surgical department: ‘We found good processes for reporting and escalating incidents and good sharing of learning from incidents. There was a good understanding of the duty-of-candour regulation and major incident policies among clinical staff.’ ”

The CQC did not comment on the ongoing investigation triggered by the “preventing further deaths” report.