Abolishing primary care trusts (PCTs) too quickly could damage patient care, a report has claimed.
The government has laid out plans to scrap PCTs in a white paper, but think tank Civitas said doing so without staggering the proposal could cause delays to treatment.
Its study - A Risky Business - calls for a more "incremental approach" to reform and it fears government hopes for large cost savings of up to £20bn could be undone if the plan is not thought through properly.
It follows suggestions that PCTs are currently in "meltdown" over the policy, which will see most of the NHS budget transfer into the hands of GPs, who will be responsible for commissioning health services for patients.
Written by James Gubb, director of the Civitas health unit, the document poses 12 questions for Cabinet Office minister Oliver Letwin, who is to scrutinise the new health policy.
It says it is "very uncertain" that the wholesale abolition of PCTs by 2013 in favour of groups of GPs will bring about significantly improved commissioning in the short, medium or long-term.
Patients are likely to suffer delays in getting treatment while the reforms are carried out and will not necessarily get improved care in the future, it says.
While the NHS has been guaranteed a small real terms increase in funding, campaigners say demand for services is putting pressure on the NHS.
To meet this demand, the NHS will have to improve productivity by around 4% per year, the report said.
However, it argues that GP consortia are more likely to be more focused on administration and structural tasks, such as merging organisations and getting the right people in place as they establish themselves.
Mr Gubb said: "The coalition government needs to stop repeating the mistakes of the past by mandating wholesale structural change."
Copyright © Press Association 2010