The plans being discussed by junior health minister Lord Darzi to effectively fine GPs when patients inappropriately use walk-in centres, accident and emergency departments and minor injury units, illuminate some of the darker corners of primary care policy.

Minor injury units and walk-in centres were never intended to replace GPs, but there is growing concern that patients are rolling up at these facilities and, worst of all, A&E, because they cannot get in to see their doctor.

The idea of diverting money away from GPs is a radical departure from the previous principle of paying them more to improve the health of their population.

On one level, the proposal is a natural extension of the payment by results principle, where the money follows the patient. As politicians increasingly focus on efficiency in the health service, it is rational to reform a system which effectively leads to double payments for someone who is registered with a GP but chooses to access services elsewhere. It is difficult to understand why this aspect of walk-in centre funding was not addressed when they were first proposed.

In theory the change now being debated as part of Lord Darzi's next stage review could gently turn the access screw, pressurising GPs to improve opening hours to reduce the need to use alternative facilities, although it is questionable whether the financial penalties will be sufficient to deliver substantial changes in opening hours.

But, as so often with the primary care reform journey, the debate is starting from the wrong place.

The subtext is, again, how to wring more value for the money squandered on behalf of the taxpayer in the GP contract negotiations of 2004.

Any changes need to avoid a serious pitfall. The areas where people are least likely to visit their GP are often deprived, and short of family doctors. It is vital that fines on GPs who do not "prevent" patients visiting other facilities do not become a strong disincentive for doctors to set up shop where they are needed most.