This work investigates the impact of pretreatment technologies in the design of BioSNG supply chains at a regional and national scale. For this purpose, an optimisation-based framework is proposed to account for two possible routes for BioSNG production. The first route considers processing of raw biomass and production of BioSNG in integrated facilities. The second route consists of pretreatment technologies, transportation of intermediate products, and upgrading facilities. The main objective is to investigate the trade-off between capital investment and reduction of transportation costs, and their impact on the economic performance of a BioSNG supply chain. Moreover, the impact of government subsidisation is further investigated through a parametric analysis in which the tariff is varied from 0 pound/MWh up to 100 pound/MWh. Finally, the major contributing factors in the design of BioSNG supply chains are identified through the implementation of a rigorous global sensitivity analysis (GSA). The results suggest that inclusion of pretreatment technologies improve considerably the economic performance, however, their impact is not enough to detach the development from government subsidisation which influences tremendously the possibility of a large-scale deployment.