NHS organisations whose blunders led to the death of a three-year-old boy had a total unwillingness to accept that any other view apart from their own was the right one, a damning report has found.
A second investigation by the Parliamentary Health Service Ombudsman (PHSO) into the death of Sam Morrish from Devon concluded it also had lessons to learn from its investigation of complaints.
Sam Morrish died in December 2010 from sepsis following a "catalogue of errors" by GPs, hospital doctors and call handlers at NHS Direct, now replaced by the 111 service.
NHS Direct call handlers failed to categorise Sam's mother's call as urgent, despite indications that his vomit contained blood.
Even when medical staff at Torbay Hospital finally realised he was critically ill, there was a three-hour delay in giving him the antibiotics that could have saved his life.
A review by the PHSO in 2014 found Sam's death was avoidable and he would have survived with proper care and treatment. But Sam's parents, Sue and Scott Morrish, called for a further investigation to find out why their son died and to ensure proper learning across the NHS.
In the latest review, the PHSO concluded there was no attempt to cover up failings in Sam's care but criticised previous investigations.
It said a "fundamental failure in this case was the organisations' - in particular the trust's - total unwillingness to accept that no view other than their own was the right one.
"Those involved appeared to accept almost immediately the view that Sam's death was rare and unfortunate rather than being open to other possibilities and, in doing so, asking open questions as part of a proper investigation that involved staff and the family.
"This was coupled with a general failure to accept that the questions the family were asking might have been reasonable ones."
The damning report detailed the confusion around giving antibiotics when Sam was admitted to Torbay Hospital, part of South Devon Healthcare NHS Foundation Trust.
It also criticised the inadequate investigations carried out by NHS Direct, the Cricketfield GP surgery, NHS Direct, and out-of-hours provider Devon Doctors.
It said: "The organisations made no clear attempt collectively to seek to identify lessons from this case.
"Without a proper investigation into the events that took place, involving the staff and the family, there was no possibility of learning (locally or nationally) or action being taken to avoid such incidents in the future."
It also agreed with Mr and Mrs Morrish on their assessment of the NHS's failings.
It said: "Mr and Mrs Morrish complained that the NHS investigation processes are not fit for purpose, believing that they are not sufficiently independent, inquisitive, open or transparent, properly focused on learning, or able to span organisational and hierarchical barriers, and that they exclude patients, their families, and junior staff in the process.
"In relation to the investigations undertaken after Sam's death, we agree."
PHSO Julie Mellor said: 'We hope that this case acts as a wake-call up for NHS leaders to support a no-blame culture in which leaders and staff in every NHS organisation feel confident to find out if and why something went wrong and to learn from it.
"The new Health Safety Investigation Branch (HSIB) is a step in the right direction, but will only investigate a small number of cases.
"We want to see a national accredited training programme for people carrying out NHS investigations and for this to include clarity about independence and accountability."
Mr Morrish said: "I hope that this report leads to rapid change in the culture of the NHS, so that mistakes can be recognised, investigated and learnt from. Anything short of that isn't safe for patients and isn't fair to NHS staff.
"I hope that no other family has to go what we have been through. Sam's death was avoidable, and the NHS should have given us the answers we needed soon after he died, to enable improvements to be made."