The chief executive of health and social care regulator the Care Quality Commission (CQC) has resigned.

Cynthia Bower said it was "time to move on" after almost four years as head of the organisation, which has been heavily criticised over the last year.

Her departure comes as the Department of Health published its findings from a performance and capability review of the CQC, stating the regulator had made considerable achievements since 2009 but that more needs to be done to improve its services.

In December, a report from the National Audit Office highlighted problems as the CQC took on the role of registering all providers of health and social care. It said the level of inspections of care homes in England fell "significantly" as a result, and the CQC had failed to deliver value for money.

That followed a report from MPs in September which found the regulator had "distorted" its priorities by focusing on registering providers. Registering organisations led to around a 70% drop in the number of inspections to check care standards and safety, it said.

The CQC has argued it was faced with the challenge of setting up an entirely new regulatory system and registering more than 40,000 provider locations against tight deadlines set by the Department of Health.

Ms Bower said: "After almost four years leading CQC, I feel that it is now time to move on. The process of setting up an entirely new system of regulation has been intensely challenging, but we have accomplished an enormous amount. I am pleased that the Department of Health performance and capability review, published today, recognises the scale of what has been achieved, and in particular the significant improvements made over the last nine months."

Ms Bower will remain in post until the autumn to ensure a smooth handover. The CQC said the recruitment process for her successor will begin shortly.

The review from the Department of Health said the CQC had delivered a challenging programme of work, registered providers and is increasing the number of inspections taking place.

However, it said the scale of this task had been "underestimated" by CQC and the department, and more could have been done to manage risks during the early years of the organisation's operation. A series of recommendations include appointing extra members to the CQC's board and creating clearer arrangements between the board and the executive to ensure that the board is holding the operation of the CQC to account.