Cyberterrorism has not occurred. Furthermore, the definitional parameters of cyberterrorism have not been conclusively defined by either policymakers or academia. However, in 2010 the threat posed by the terrorist application of cyber weaponry to target British critical national infrastructure became a ‘Tier One’ threat to the UK. This thesis is the first comprehensive mapping and analysis of the official British construction of the threat of cyberterrorism between 12th May 2010 and 24th June 2016. By using interpretive discourse analysis, this thesis identifies ‘strands’ from a comprehensive corpus of policy documents, statements and speeches from Ministers, MPs and Peers. This thesis examines how the threat of cyberterrorism was constructed in the UK, and what this securitisation has made possible. In addition, this thesis makes novel contributions to the Copenhagen School’s ‘securitisation theory’ framework. Accordingly: this thesis outlines the framework for a ‘tiered’, rather than monolithic audience; refines the ‘temporal’ and ‘spatial’ conditioning of a securitisation with reference to the unique characteristics of cyberterrorism; and lastly, details the way in which popular fiction can be ascribed agency in securitising moves to ‘fill in’ a lack of case studies of threat with gripping vicarious fictional narratives. It is identified that the 2010 British Coalition Government’s classification of cyberterrorism as a ‘Tier One’ threat created a central strand upon which a discursive securitisation was established. Despite the absence of a ‘cyberterrorist’ incident across the period under scrutiny, the securitisation did not recede. The threat posed by cyberterrorism was articulated partially within a ‘New Terrorism’ frame, and it was deemed by Ministers, MPs and Lords to be a threat that was likely to escalate in both severity and possibility over time. A notable finding is the positioning of the securitisation against a particular ‘cyberterrorist’ identity epitomised by social actors using cyberspace, rather than the tangible environments of cyberspace.