This paper presents a critical comparison of a virtualised data centre infrastructure and an infrastructure that consists of physical servers. Our investigation shows how virtualisation can better utilise the hardware and consequently reduce the power consumption and carbon emissions. The case study reports an extensive research phase to identify main reasons for data centre virtualisation. The data centre is then modelled, based on server information from one of the data centres at the University of Greenwich. We emulate a virtualised infrastructure to contrast against the physical infrastructure. These two models are then critically compared and the potential carbon emission reductions and savings are analysed. Our results show that a virtualised data centre infrastructure can potentially reduce carbon emissions by approximately 30%.