Bioenergy has an important role to play in helping the UK meet its carbon target in 2050 and the European Renewable Energy Directive objectives for 2030. There are however uncertainties associated with the use of bioenergy, and whether or how much it contributes to green-house gas emission reductions. In order to help identifying environmental benefits and burdens associated with biomass use for energy production, an attributional life cycle assessment has been carried out of a biomass-fired CHP plant: the Heathrow Airport energy centre. This facility burns woodchips sourced from nearby forests providing 2 MWe of electricity and 8 MWth of thermal energy which delivers heat and cooling to Heathrow Terminal 2 and low temperature hot water to Terminal 5. A hot spot analysis is conducted to identify the process steps with the largest environmental impact, starting from the harvesting of the forest residue to the disposal of the boiler ash. A scenario analysis is performed to compare the impacts of the biomass plant against fossil alternatives and to identify which renewable energy sources, between biomass and MSW, should be prioritised for development and investment. The results show a reduction in GHG emissions from using biomass, with further benefits if the bottom ash is collected and re-used as a soil conditioner for land-farming or forestry. The paper also discusses the treatment of biogenic carbon in the assessment. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.