A report from the Public Accounts Committee into use of agency staff found that over 1,000 former RUC officers returned to serve on a temporary basis - some just days after leaving.It said the practice has cost an "excessive" £106m since 2004.Committee chair Michaela Boyle MLA said: "By taking its eye off the ball, the PSNI has spent considerably more than was necessary on agency workers."The report found that there are "sound operational reasons" for employing temporary staff in the PSNI, adding that while some roles require policing skills, many others do not.It criticised a "lack of accountability" of agency workers filling policing roles and noted that there is no power for the Police Ombudsman to regulate their conduct.Ms Boyle, of Sinn Féin, continued: "This report has identified a number of issues that concerned the committee."Proper competitive arrangements, which would have ensured value for money, were not put in place until 2008. The current supplier has been in place since 2002, establishing a virtual monopoly in the supply of temporary staff to the PSNI."Moving forward, any new contracts awarded by the PSNI must be subject to proper options appraisal and business cases and have the approval and authority of the Policing Board."A statement from the PSNI said the report "rightly" sets its findings in the context of "unprecedented" change to Northern Ireland's police service in the wake of Patten, adding that around 8,000 officers and 2,323 police staff left between 2001 and 2011."This change is without parallel in world policing," the statement said."The Chief Constable notes a number of concerns which the committee has raised in relation to the accountability arrangements and governance of the use of agency staff and fully accepts that there should have been greater scrutiny and oversight of the arrangements in past years."However the PSNI has provided reassurances to the Committee that any shortcomings have been addressed and, since January 2011, there has been an extremely robust, centrally monitored process in place for the appointment of temporary staff."