As details emerge from the health White Paper, Equity and Excellence: Liberating the NHS, about the coalition government’s plans to reform the NHS by handing general practitioners more commissioning power, one thing is certain: this reform is high risk and will need very careful implementation if it is to deliver where others in the UK and overseas have failed.

With this in mind, we’ve come to the United States to find out about one type of clinician-led organisation that is similar to the proposed GP commissioning groups. In California, some GPs and specialists work in large medical groups or networks that bring together small practices to hold budgets for some or all of the health care that their patients will need.

These groups receive a monthly fee from the insurance company (or the federal government in the case of Medicare for older people) from which to provide both primary and hospital services. This is the first powerful incentive – it is in the financial interest of these groups to see that patients are kept well and not admitted to hospital unnecessarily.

The success of these groups, some of which have hundreds of thousands of patients, depends on their ability to support and enable doctors to practise good and appropriate medicine and to co-ordinate care with other parts of the health and social care sector.

The organisations closely manage the performance of their doctors. High quality care is rewarded with bonuses, poor performers are supported to improve, but eventually, poor-quality care can lead to exclusion from the medical group.

Many of these groups have hired social workers, specialist care managers and hospital-based doctors who make sure that their frailest patients are supported to leave hospital with an appropriate range of support services and so are at minimal risk of re-admission. These groups now boast readmission rates as much as 60 per cent lower than the national average.

Judging from this evidence, it is easy to see why the coalition government might be excited by the California model. Business savvy doctors have been able to devise new forms of care that have cut a profitable swathe through the highly wasteful US health care system in a way that benefits patients.

But there are some important caveats here that the new government would do well to heed. These groups have invested substantially in management infrastructure, including IT systems and the expertise needed to monitor quality and negotiate multiple contracts with providers. They have also invested in leadership and are training the next generation of physician leaders to take over from the original trailblazers. Time away from seeing patients is always reimbursed and much time has been devoted to building relationships with hospitals and specialists, and although this is a competitive market, in practice, contracts are rarely switched.

These groups have also taken decades to evolve in a generally favourable financial environment which has seen steady increases in the budgets allocated for the care of a patient each year.

And above all, these groups are the survivors. Many smaller groups who set out on the budget-holding and commissioning road went bust both in California and in the rest of the US. The ones that have thrived have done so with a fair financial wind and a business-oriented culture that accepts failure. These conditions are not currently present in the NHS. The reforms will need to be carefully designed and implemented in the light of these constraints.

There are clearly a great many details still to be worked out in England- these challenges are summarised in our recently published paper Giving GPs budgets for commissioning: what needs to be done?