This document introduces a novel access control architecture for publicly accessible wireless overlay networks. The architecture is designed to address the problems of ubiquitous Internet service provisioning within the city of Lancaster. The proposed access control mechanism is based on the concepts of secure user authentication, packet marking, and network-level packet filtering. The novelty of the architecture lies in its use of micro-cellular layer three networks to acquire fine grained access control in a link independent manner. The paper describes the concepts behind the access control architecture and demonstrates to what extent it addresses the security, performance and extensibilityconcerns of public access packet switched wireless networks.