The new building in Little France was due to open earlier this month but was delayed by health secretary Jeane Freeman after it was found that the ventilation system within the critical care department in the new hospital requires further work to meet national standards.

The much-delayed project replaced facilities for children at Sciennes near the centre of Edinburgh, and at the Western General Hospital and Royal Edinburgh Hospital, with a purpose-built complex.

The hospital was originally supposed to be open by the winter of 2012, only to be held up by a protracted land swap deal.

Work then began on the project with an initial opening date of autumn 2017, but this was again put back due to contractor liquidation and delays caused by factors including bad weather.

Now architect Robert Menzies, who said he warned of the facility’s design flaws two years ago, has claimed political pressure to avoid further delays meant those in charge of the project were not willing to take time to make changes.

Mr Menzies, who has 40 years’ experience building hospitals, said he highlighted a failure to include a larger lift to accommodate orthopaedic patients needing to be moved with equipment, a child protection suite with a corridor separating two rooms intended to have a one-way mirror between them and classroom doors too narrow for beds to get through.

The architect claimed he warned of issues in other areas of the building but was ignored or overruled.

“I witnessed a decision-making process which repeatedly placed the need to meet deadlines ahead of patient safety,” he told the Edinburgh Evening News.

Mr Menzies said he had warned the “reference” design for the hospital – drawn up with clinicians to let those bidding for the hospital contract know what was required – needed an additional three months’ work to make it viable, but that was refused because “a further delay was politically unacceptable”.

He said insistence on sticking rigidly to the reference design when it had not been properly finalised led to lots of problems.

Susan Goldsmith, finance director and former acting chief executive of NHS Lothian, said: “The disappointing current delay to the new Royal Hospital for Children and Young People and Department of Clinical Neurosciences and the Child and Adolescent Mental Health Service has been caused by issues that are completely unrelated to any of the points made by Mr Menzies.

“The delay is caused by a problem with ventilation in critical care, which was identified during the final checks.

“Further tests are being carried out in all clinical areas and in a further sample of general areas to gain additional assurance that the required standards are met.”

The Scottish Government has now ordered a detailed assessment of compliance of all building systems at the facility to guarantee the safety of patients and staff.