In this paper existing epidemic models of diffusion in the literature are modified to give freer interaction between exogenous and endogenous factors in the diffusion process and to also reflect the role of economic factors in that process. A new encompassing model is proposed and its properties explored. The model is applied to the diffusion of colour television ownership in the UK and outperforms the existing models in the literature. The exogenous factors play a dominant role in the diffusion of colour television in the UK.