The Nursing and Midwifery Council failed to properly investigate 17 former nurses at the Mid Staffordshire Foundation Trust according to an audit by the Professional Standards Authority.

The PSA, which oversees professional regulators, has reviewed 100 instances where the NMC closed cases at an early stage of investigation.

Its report, published today, reveals a series of errors and says it has “serious concerns” that the “wrong decisions” may have been made about cases.

The findings follow concern about professional regulators’ actions in relation to Mid Staffs and other major care failings.

The report says some of the decisions call into question the effectiveness of the NMC and may have put patients at risk.

The PSA audit included 19 nurses who worked at Mid Staffs, 17 of which related to poor care highlighted during Robert Francis QC’s public inquiry.

In nine of the Mid Staffs cases the report said there was no evidence of the NMC carrying out a risk assessment. It said the NMC did not investigate concerns or carry out proper investigations to find more information from sources such as the coroner, trust or the public inquiry.

In one example a case was closed on the basis there were no complaints about the nurse – despite two complaints “clearly on the NMC file”.

On another occasion, the report said, the NMC closed an investigation solely on the basis of an unsigned positive reference about a nurse on headed letter paper, with no attempt to check its accuracy.

The report said: “Our audit identified a number of serious concerns about the relatively limited extent of the investigation that the NMC conducted.

“The evidential basis for some of the decisions made by NMC staff and the [investigation committee] was inadequate. This meant that either the wrong decision was made and/or the decision that was made was based on unsound or inadequate reasons.”

The report identified delays in the NMC applying for interim suspension orders to prevent nurses working unsupervised while under investigation in five cases, which “may have exposed the public to unnecessary risk”.

The PSA report said it found some problems which “[call] into question [the NMC’s] effectiveness as a regulator”.

However, it said the NMC had improved in some areas, and its investigations did not lead it to have concerns about public protection.

NMC chief executive and registrar Jackie Smith said: “We know that there is still more we need to do. However, it recognises the progress we have made and confirms the commitment we made to improving performance.”