The government must not dictate how to develop integrated care systems following Lord Darzi's forthcoming review, a leading health policy organisation warns.

In the report, Integrating NHS Care: lessons from the front line, the Nuffield Trust argues that government policy following the Darzi review "needs to recognise that there are different routes to integration".

The concept of integration has become an important strand of the Department of Health's commissioning strategy, with last December's operating framework spelling out that vertical integration - for instance a foundation trust providing primary care services - would be "permissible" when in the best interests of patients and taxpayers.

But the Nuffield Trust report warns that while fundholding schemes and locally negotiated GP contracts were found to have helped facilitate a wider range of models of care outside hospital, practice-based commissioning had "failed to offer an equivalent stimulus". It adds that a major challenge will be to reconcile clinical integration with patient choice.

The report analyses three integrated care models: a diabetes centre which employs a community specialist team, a diabetes, diagnostics and day surgery unit established under GP fundholding, and a PCT/acute trust joint working initiative inspired by Kaiser Permanente.

The models exemplify three different routes to integration: community-based specialists, primary care reaching into hospitals to provide more care in the community and partnership between primary and secondary care.

Chris Ham, professor of health policy and management at Birmingham University and author of the Nuffield Trust report, said: "The department shouldn't come out with a prescribed route to integrated care. It should encourage clinicians and managers at a local level to do that but find the best way of so doing."

Professor Ham added that the DH must also commit to evaluating the impact of integrated care systems on patient care. In addition, practice-based commissioning consortiums needed stronger incentives and more responsibility in order to drive change, he said.

But he stressed that integrated models could work as an additional factor in patient choice: "At the moment, patients choose their GP practice. As integrated care arrangements evolve, they would be choosing their GP and the integrated care organisation it was a part of."

A spokesperson for the DH said: "We cannot pre-empt the outcome of the next stage review, but we recognise the need for flexibility, and the importance of evaluating new models, to develop the best services for local needs."