The cost of delays to the opening of Edinburgh’s new children’s hospital will add up to an additional £28m, it has emerged.

Scotland’s public spending watchdog revealed the figure in a report published today which says key questions around the failure to open the site remain unanswered.

Audit Scotland raised concerns over why issues which emerged at Glasgow’s Queen Elizabeth University Hospital (QEUH) – which involved the same contractor - did not prompt greater scrutiny.

NHS Greater Glasgow and Clyde has now launched legal action against the contractor, Brookfield Multiplex.

A public inquiry into construction issues at both hospitals, chaired by Lord Brodie, is due to get underway next year.

The opening of the Royal Hospital for Sick Children & Young People was called off at the last minute in July after final checks revealed a critical care ventilation system did not meet standards.

The Audit Scotland report says reviews to date, carried out by KPMG and NHS National Services Scotland (NSS), have been unable to establish answers to number of issues.

This includes why the hospital’s 2012 tender papers were inconsistent with national ventilation guidelines for critical care – an error which ‘led to confusion’.

A series of opportunities to spot the error, which led to the delayed opening of the hospital, were also missed.

The additional cost of work required to ensure the hospital complies with standards and keeping the current site open while this is done is now expected to be £28m.

A breakdown of the costs shows this includes payment of £11.6m to developers IHSL to facilitate resolution of ‘key outstanding technical matters’.

The work to rectify the ventilation issues will cost £4m, while the dual running and additional maintenance at the two sites adds up to £3.5m.

Caroline Gardner, auditor general for Scotland, said it was clear checks and balances around the construction of the hospital did not work.

 “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.”

A spokesperson for the Royal College of Physicians of Edinburgh said the report indicated some “clear oversights” and raised questions around levels of scrutiny.

“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.”

Health secretary Jeane Freeman said the KPMG and NSS reports would provide a “significant amount of underpinning evidence” for the public inquiry, along with an ongoing independent review into issues at the QEUH.

She said the public inquiry would help 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.

“In the meantime, 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.”