Key questions around the delayed opening of Edinburgh's troubled new children's hospital remain unanswered, Scotland's public spending watchdog has said.

The Auditor General for Scotland said two reviews already carried out into the botched opening of the £150m Royal Hospital for Children and Young People (RHCYP) have been unable to clarify certain issues.

Audit Scotland's own report, published on Wednesday, outlines these outstanding questions, including why specifications in the hospital's 2012 tender papers were inconsistent with ventilation guidelines for critical care wards.

The paperwork blunder resulted in confusion, while a "series of opportunities" to spot the error were missed over the next seven years, the Auditor General noted.

The watchdog's report draws on a review already carried out by NHS National Services Scotland (NSS), which performed water, ventilation and drainage checks across the state-of-the-art hospital, located in Little France.

It didn't find any "widespread contamination" but pointed to inadequate ventilation in its critical care unit - where patients with life-threatening conditions, who may require major surgery, are treated.

NHS NSS noted any contamination in this unit could be fatal for patients, with fixing the problem expected to add another £16m to the cost of construction.

The report also uses the findings of a further review by KPMG into governance arrangements around the hospital's construction as well as NHS Lothian's annual audit report.

The 242-bed RHYCP was supposed to open in July but saw its launch vetoed by health secretary Jeane Freeman at the 11th hour. It is now hoped it will open its doors in the autumn next year.

The health secretary subsequently announced a wide-ranging public inquiry into issues both at the Edinburgh hospital and Glasgow's Queen Elizabeth University Hospital (QEUH) and Royal Hospital for Children (RHC), whose "super-hospital" campus opened its doors in 2015.

The Glasgow site has been plagued by questions around infection control after the deaths of two children on a ward which had been affected by water contamination.

On Tuesday, NHS Greater Glasgow and Clyde revealed it would be taking legal action against Brookfield Multiplex, contracted to design and build the hospital, which was also involved in the construction of the RHCYP.

Caroline Gardner, Auditor General for Scotland, said: "It's clear that the checks and balances around the construction of the new children's hospital didn't work, and the public inquiry may want to consider why that happened after similar issues had emerged around the building of schools in Edinburgh.

"It would also be beneficial to understand the role played by all the parties involved, and to explore why the issues that emerged at Glasgow's Queen Elizabeth hospital didn’t prompt greater scrutiny in Edinburgh."

Freeman said: “I’d like to thank Audit Scotland for this report, which recognises the crucial role of the independent public inquiry into issues at the RHCYP in Edinburgh and the QEUH campus in Glasgow.

“The KPMG and NSS reports into the RHCYP will provide a significant amount of the underpinning evidence for the inquiry, alongside the ongoing independent review into the delivery and maintenance of the QEUH.

“As I announced last month, Lord Brodie will chair this independent public inquiry, which will help us learn lessons from recent issues so they are not repeated in the future.

"I have a statutory obligation to consult with the chair on the inquiry’s terms of reference and I will provide a further update to parliament early in the new year."

She added: "NHS Lothian continue to provide high-quality care from the existing sites, and I want to thank staff, patients and their families for their continued patience as we work to migrate services to the new site as soon as it is safe to do so. Patient safety will always be my top priority.”

A spokesman for the Royal College of Physicians of Edinburgh said: “Serious failings at hospitals in Scotland in recent years have highlighted the need for quality governance in healthcare, with patient-centred decision making at its heart.

"Indeed, Audit Scotland have indicated some clear oversights and have highlighted questions around levels of scrutiny in their latest report.

"The College believes that the Audit Scotland report further highlights the need for reinforced governance arrangements.

“In Scotland, this is an area where we’d like to see the Scottish Government play a leading role, working with NHS Boards and clinicians to develop more meaningful performance indicators in relation to the quality of care."