Electrifying the energy system and powering it by low carbon electricity is one of the key decarbonisation pathways of the energy system. This study examines annual electricity and gas consumption in a high electrification scenario in Great Britain (GB) and the implications for electricity generation and transmission infrastructure using a suite of soft-linked models. High electrification of heating and transport services, which are two major fossil fuel consumers in GB, increases annual electricity consumption and peak electricity load by 35% and 93%, respectively, by 2050 while reducing overall annual energy consumption compared to a reference case. Meeting this high electricity consumption with a supply strategy that is dependent on offshore wind could more than double the supply-side investments required compared to a reference case, if demand-side measures are not available. High electrification would also impact existing gas and oil energy infrastructure by reducing consumption of these fuels. It was found that uncertainties in socio-economic growth can amplify these implications and therefore need serious consideration by analysts and policymakers involved in designing energy transition strategies. A case study and discussion demonstrate that smart-grid aided demand-side management has the potential to minimise electricity peak load and infrastructure requirements from high electrification.