Abstract-Spectrum sharing has been the subject of a 3 year research programme organised by the UK's Virtual Centre of Excellence in Mobile and Personal Communications. Cognitive radio was identified as a key enabling technology to allow spectrum to be shared efficiently between terminals and networks. The project has harnessed the skills of 4 UK Universities working together to understand the potential benefits for its industrial members of cognitive radio technology. This paper discusses some of the work that has been carried out by the Mobile VCE researchers in the field of cognitive radio together with some of the key results and conclusions. The central work has developed algorithms that control the dynamic allocation of radio resources between cooperating network operators as well as spectrum access protocols that allow suitably equipped terminals to sense and use free spectrum. Simulation work has shown that a gain in the efficiency of spectrum use is feasible for both types of spectrum sharing.