Almost £6 million worth of maintenance work carried out by contractors for the Northern health trust since the turn of the century was not properly accounted for, a Stormont probe has found.
Health Minister Edwin Poots said the findings of an audit investigation, which identified failings in procurement practices and accounting control within the Northern Health and Social Care Trust (NHSCT), were a "matter of serious concern".
Allegations of potential malpractice were made by whistle-blowers in 2012.
The subsequent investigation concluded that there was "no clear evidence of fraudulent activity" or no incidences of contractors being paid for work they did not do.
But the auditors did identify a series of weakness in the estates management function of the trust that meant it could not be established if expenditure on maintenance contracts represented value for money.
"The total value of work that has not been subject to appropriate control or procurement is estimated as £5.7 million over the past 14 years," Mr Poots revealed in a written statement to the Assembly.
"This is a matter of serious concern."
Examples of weaknesses in the implementation of procurement controls and guidance found within the trust included:
:: Single Tender Actions awarded without formal approval.
:: A contractor working without a contract for several years.
:: Contractors used outside of their contracted areas.
:: Documentation missing from files to verify expenditure.
:: Lack of checks on work carried out and invoices presented for payment.
:: Contracts being completed in excess of tender quotation due to additional work undertaken.
The report made 72 recommendations.
"The trust has made significant progress in implementing the recommendations to date," said Mr Poots.
Mr Poots said audit checks would be carried out across the other trusts in Northern Ireland to ensure that similar practices were not occurring elsewhere.
He added: "The mismanagement of procurement and contract management at NHSCT was brought to the attention of NHSCT and my department through the whistle-blowing process.
"And, once again, I want to say that it is appropriate and important that where anyone has information about the potential abuse of public money they inform their organisation or my department so that the specific issues can be resolved, appropriate lessons learned and public confidence restored.
"Where wrongdoing has occurred it must be addressed, with a proportionate and appropriate response.
"NHSCT management are assessing the reasons behind the failures identified in the report and an independent review will consider whether any further action is appropriate."
SDLP MLA John Dallat said it had taken almost two years to compile a report.
"As a long-serving member of the Public Accounts Committee, it astounds me that the wrong-doing and bad practice referred to in the minister's statement have been highlighted time and time again across different government departments, including the Department of Health, with promises given that things would change, that the spending of public money would be squeaky clean and people could have confidence in those accountable," he added.
"Regrettably, here again we have the same promises trotted out but, quite frankly, there is little credibility in those assurances."
Sinn Fein MLA Oliver McMullan said: "I am shocked by the level of failure in the awarding, overseeing and in the accountability of building maintenance contracts across the Northern Trust area. There are serious questions to be answered by those in charge at the Northern Trust.
"It is a concern that £5.7 million of much-needed money can be frittered away. This at a time of ever diminishing resources and tighter budgets in the health sector.
"The minister needs to take action as it is obvious the current management oversight mechanisms are not fit for purpose."