The introduction of a WCDMA microcell layer has implications upon inter-operator coexistence. Coexistence has been studied extensively throughout 3GPP standardisation to help ensure the appropriate specification of adjacent channel performance. The majority of 3GPP studies have been based upon theoretical radio network plans with regular street and building layouts. The paper provides an analysis of inter-operator inter-layer coexistence based upon a realistic radio network plan in central London. WCDMA simulations have been completed to provide a detailed analysis of the various system interactions and impact upon system performance.