The UK government has pledged to reduce its greenhouse gas (GHG) emissions by 80%, from 1990 levels, by 2050. Decarbonisation of transport and heat supply to buildings is recognised as a fundamental step in achieving this target. With cities being the largest producers of GHG emissions they provide the biggest opportunity for climate change mitigation. Two contrasting visions of a 2050 target-compliant scenario are evaluated against each other. One is based on a high penetration of nuclear power and renewables the other based on predominantly gas with carbon capture storage (CCS). An impact assessment is carried out on both scenarios to understand how each scenario might perform over 4 evaluation criteria. The evaluation criteria provide insight into each scenario regarding; guaranteeing security of supply, scenario cost, sustainability and how feasible it is to deploy the chosen technologies. Whilst both scenarios raise discussion points on the feasibility of deploying certain technologies the more favourable scenario, in terms of the study results, is the nuclear and renewables option. The renewable energy generating technologies included as part of the study from largest to smallest in terms of capacity - are wind, solar photovoltaic, tidal and river hydro. The outputs of this study provide an important contribution to academic debate on what might be the most effective approach to achieving the 2050 decarbonisation target. (C) 2019 Elsevier Ltd. All rights reserved.