Public confidence in the Care Quality Commission was weakened last year when the body failed to address issues raised by board member Kay Sheldon, MPs said.
They said that it was "regrettable" that Ms Sheldon was forced to voice concerns about poor leadership and safety breaches at the regulator at the public inquiry into failings at Mid Staffordshire NHS Foundation Trust.
The report states:
The decision by CQC board member Kay Sheldon to give evidence as a whistle-blower to the Mid Staffs Public Inquiry added to the controversy surrounding the CQC.
She identified serious failings within the management, organisation, functions and culture of the CQC.
Kay Sheldon's concerns were legitimate and it is unacceptable that the CQC failed to address and act on them before she felt compelled to approach the public inquiry.
The outgoing chair of the CQC was grilled about her handling of Ms Sheldon when she appeared before MPs in September last year.
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