Care Quality Commission chief executive Cynthia Bower has resigned.

She has announced her resignation on the same day the Department of Health has published the findings of its “performance and capability review” of the regulator.

The review found the CQC had made “considerable achievements” since it was established in 2009.

But it said the challenge of registering more than 21,000 providers had been “underestimated”  by the CQC and the DH, and more could have done more to manage risks during the early years of the organisation’s operation.

The review also said the role of the CQC has “not been as clear as it needs to be to health and care providers, patients and the public”.

It says a review of the regulations underpinning the regulator’s work is due to conclude “shortly”, with new regulations laid before the Easter recess. A second, “more comprehensive” review is about to start.

This will “look at the regulations as a whole to ensure the framework is proportionate in minimising the risks to people who use services; it will examine the extent to which CQC regulation can mitigate that risk. The review will address issues where the regulations are not supporting an effective proportionate regulatory framework.”

As part of this review, the department will consider “any relevant recommendations of the Mid Staffs Inquiry, and the public accounts committee and health committee reviews of CQC”. It will also “consider the effect of changes to the architecture, such as those coming out of the Health and Social Care Bill”. The department will be consulting formally on proposals later in the year.

The review has made 23 recommendations, including for the CQC to revise its strategy, improve its analytical capacity, develop its performance measures and strengthen board structures.

Another recommendation is for the DH, through the National Quality Board, to develop “explicit statements as to the distinctive roles of national bodies in assuring quality and providing incentives for quality improvement - the ‘who does what’ for quality”.

Ms Bower will remain in post until autumn 2012. The recruitment process for her successor will begin “shortly”.

In a statement, she 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. We have merged three organisations, registered 40,000 provider locations and brought virtually the entire health and social care network under one set of standards, which focus on the needs of people who use services.

“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. I’m confident that CQC will continue to build on the progress already made, delivering  increasing benefits to people who use services by shining a light on poor care - and I am proud to have played a part in this.”

CQC chair Jo Williams said: “I am very sorry that Cynthia has decided to move on, but I understand her desire to take on new challenges. I would like to take this opportunity to thank her for the enormous contribution she has made to the setting up and running of CQC.

“She has shown tireless commitment to this organisation, and she leaves it in a strong position to carry out our essential role in tackling poor care. This is confirmed by today’s performance review from the Department of Health, which recognises the CQC’s ‘considerable achievements’ in setting the essential platform from which tougher regulatory action can be taken,” she added.

NHS chief executive Sir David Nicholson said: “I would like to thank Cynthia for her commitment as CQC chief executive. Building a new regulator involves great vision, leadership and resilience. This is always a complex task and one under constant scrutiny. It is great credit to Cynthia’s leadership to have achieved this.”

DH permanent secretary Una O’Brien, who has been carrying out the review, said: “Cynthia has provided energetic leadership to the CQC from its very outset.  Over her four years as chief executive, CQC has introduced - for the first time - a new model of regulation for health and social care.  Cynthia is a committed public servant and I wish her well for the future.”

Health Secretary Andrew Lansley said: “I would like to thank Cynthia for her work and leadership and wish her the best of luck for the future. Over the last year, we have seen CQC make improvements and respond to the need for enhanced scrutiny and enforcement of standards.”

The CQC and Ms Bower have been heavily criticised in the past year, during the public inquiry into failings at Mid Staffordshire Foundation Trust and in reports by the Health Committee and National Audit Coffice. Ms Bower previously monitored the trust when she was chief executive of NHS West Midlands.