A hospital trust with a "toxic" culture compared to the "mafia" has been criticised for being "defensive" and unwilling to cooperate with safety reviews.
It comes as there are further claims that there were "very serious" patient safety issues at University Hospitals Birmingham (UHB).
UHB, which is one of England's biggest hospital trusts, has already come under scrutiny after allegations that doctors were threatened for raising safety concerns.
The trust denies this and says its "first priority is patient safety".
NHS England in the region is overseeing the reports on the culture, leadership and patient safety issues at UHB.
The ombudsman has since raised concerns about the reviews' transparency and independence.
He found "very serious" patient safety issues at UBH based on the trust's response to their recommendations.
In letters between NHS England, the trust and the ombudsman Rob Behrens seen by the BBC - he wrote: "PHSO's (Parliamentary Health Service Ombudsman) exclusion from the review process leaves me concerned about the completeness and transparency of the reviews."
Mr Behrens was so concerned about patient safety that he triggered an "emerging concerns protocol".
He told Newsnight: "This is the first time that I have done it. So that represents the seriousness with which we regard these issues."
He added: "It's illustrative of the defensive behaviour which undermines the credibility of the trust in the first place."
It comes after more than 50 medics, including some with decades of experience, came forward to criticise a 'toxic' working culture at the trust.
Some of the most serious allegations included how whistleblowers who were concerned about patient safety were silenced with threats of disciplinary action, BirminghamLive previously reported.
Figures from the watchdog show that there are more complaints about UBH in the past three years than about any other trust.
Mr Behrens' finding of "very serious" patient safety issues at UHB is based on the trust's response to the ombudsman's recommendations and findings, including a case of avoidable patient death, it was reported.
In a letter to the hospital trust, Mr Behrens said he was concerned by leaders' "defensiveness".
A previous investigation by BBC Newsnight and BBC West Midlands heard from former and current clinicians of the trust that accused the leadership of being "mafia-like".
The trust has previously denied this allegation.
In a report released on Friday, David Melbourne, the chief executive of Birmingham and Solihull Integrated Care Board (ICB) said "there are no fundamental safety issues at the trust" but that "there are substantial issues around culture, behaviour, leadership and governance that will need to be addressed".
A spokesperson for University Hospitals Birmingham told the Mirror: “The Chief Executive has responded to the PHSO’s letter, to provide reassurance that their concerns have been taken seriously and we have been working to arrange further meetings to agree on how our organisations can work better together in the interests of our patients and staff.
“We are committed to working with the PHSO, to ensure that all families have a clear understanding of any issues relating to their loved one’s care.”
NHS England in the Midlands told the Mirror: "The reviews into University Hospitals Birmingham Trust have been commissioned to rigorously scrutinise leadership and culture in the organisation to ensure they are providing safe care for patients, as well as providing transparent information on any areas where support and challenge are needed at the trust.
"We welcome the offer of support from the ombudsman's office who we have recently met, and we are continuing to work with them to use their expertise where it can offer the most value as part of the planned cultural review."
