The chief executive of health and social care regulator the Care Quality Commission (CQC) has resigned, it was announced today.
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 publishes its findings from a performance and capability review of the CQC.
It said the regulator had made considerable achievements since 2009 but 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.
Some 6,840 site visits to providers were undertaken in the six months between October 2009 and the end of March 2010, but only 2,008 were carried out in the same six-month period in 2010/11 - a 70% drop.
Care homes for adults received 10,856 inspections in 2009/10 but only 3,805 in 2010/11, a 65% drop.
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 today: "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."
Jo Williams, chairwoman of the CQC, 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."
Sir David Nicholson, NHS chief executive, 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."
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.
Today's 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 done more 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.
In a letter to Jo Williams, the Department of Health's Permanent Secretary Una O'Brien, said: "Over the last nine months, CQC has made significant improvements in performance and in focus on core purpose.
"However, the evidence has clearly shown there is more work to do to build on recent successes to ensure the organisation has the capability and capacity to respond to patient, public and Parliamentary expectations in the future. Lessons need to be learned from the performance shortcomings of the early years.
"The leadership of the organisation are willing to listen and act on issues raised about the organisation's performance."