We present a policy-driven trading framework for market-based spectrum assignment. Our work allows spectrum consumers to get exclusive access rights through payment of a fee, for a given period of time, and for a given frequency band and location. The key motivation behind our proposal stems from the increased complexity of new spectrum management strategies and the need for extracting the maximum benefit from the available spectrum. In this paper we demonstrate that a policy-driven solution is applicable for the management of spectrum markets, and we present a decentralised and lightweight framework for implementing such markets in networked environments.