Contemporary efforts to promote population health improvement and to reduce inequalities in the UK are characterised by their complexity as they engage with a multiplicity of agencies and sectors. Additionally, the emphasis on promoting evidence-based practice has challenged evaluators tasked with collecting and interpreting evidence of impact in complex local health economies. National policy makers, local implementers and other stakeholders will have varying perspectives on impact and the Labour Government's centralising tendencies have acted to 'crowd out' local voices from the policy process. Drawing on the national evaluation of Health Action Zones (HAZ) this article 'gives voice' to local stakeholders and their perceptions of impact. Informed by a Theories of Change perspective, we explore HAZ interventions to articulate the nature of impact and its limits. We analyse the claims made by local HAZs with reference to the evidence base and examine their significance in the context of overall HAZ objectives. We conclude that local implementer perspectives are no less sophisticated than those at the policy centre of central government, but that they are informed by three important factors: the local context, a need to be pragmatic and the limited potency of evidence in the public policy system. (C) 2004 Elsevier Ltd. All rights reserved.