Up to 300 staff could be seconded from frontline NHS jobs to the Commission for Health Improvement, which was given its official launch by prime minister Tony Blair this week.

CHI director Dr Peter Homa told HSJ that he wants to employ 'between 200 and 300' staff on secondment, although CHI will start work next April with a core team of 'about 40 staff '.

'We are concerned to have as broad a base as possible, including experience of providing and managing healthcare as well as reviewing it, ' said Dr Homa, former chief executive of Leicester Royal Infirmary trust.

NHS Confederation chief executive Stephen Thornton said he was 'very pleased' that most of CHI's staff would be seconded from the NHS. 'We need people who have credibility and who will be missed back in the organisations they leave.'

Ministers have given CHI a£7m budget and ordered it to tackle cancer services and clinical governance in its first year.

Health secretary Alan Milburn said: 'For the first time the whole of the NHS will be subject to external investigation of its services.

'The commission will review every hospital and primary care group in the country within the next four years and publish the results.'

But Dr Homa said CHI planned to inspect only 25 trusts in its first year and no PCGs.

Inspectors will have just three years to visit more than 420 other trusts, 481 PCGs and 22 local health groups in England and Wales.

Admitting that it was 'a demanding programme of work', Dr Homa said CHI had yet to define its working methods.

But he rejected suggestions that the commission's first 25 visits would focus on the most troubled trusts.

'We want to make sure that we have a balanced caseload, ' he said.

Mr Milburn failed to reassure critics concerned that CHI will spark as much opposition among health professionals as the much-criticised schools watchdog Ofsted has among teachers.

In a clear reference to Ofsted, Mr Milburn said: 'Other public bodies - such as schools, colleges and social services - are already scrutinised to spread best practice and identify where things are going wrong.'

But Dr Homa insisted that CHI would be different from existing regulators.

'The commission is a new and unique organisation. I am not aware of any parallel organisation that adequately mirrors our style and programme of work.'

'My chair, Dame Deirdre Hine, and I are very clear that our intention is to work in a collaborative and supportive manner with staff and patients.'

British Medical Association chair Dr Ian Bogle welcomed CHI's role as a 'supportive' body.

'We expect the main thrust of what the commission would advise is to try to correct any shortcomings by educational means if at all possible.'

Dr Homa said the commission had been set up to reassure patients after 'a number of clinical scandals', such as the Bristol babies' deaths, had 'rocked' public confidence in the NHS.

But it could not guarantee a scandal free future. 'We will do our best to identify areas of concern, but like auditors we can't give a complete assurance that there will never be anything wrong.'

As well as conducting inspections of trusts and PCGs, CHI will 'investigate serious clinical failures' and 'share good practice, supporting the development of effective clinical governance across England and Wales'.