In this report NIRAB tackles the question “What Research, Development and Innovation (RD&I) is needed for the UK to deliver a High Temperature Gas Reactor (HTGR) Demonstrator by the early 2030s?”. To answer this NIRAB has interpreted the question as meaning the Demonstrator reactor should couple electricity production with high heat output, to be utilised in industrial applications. Hence, five key areas have been identified as needing investment and RD&I has been categorised as either ‘essential’, ‘highly valuable’ or ‘valuable’. The report also covers the several industrial sectors in the UK which could be assisted in decarbonisation via using heat outputs from an HTGR.