The clash between national security and civil rights comprises one of the most controversial aspects of counter-radicalisation strategy. Analysts present this as a conflict between the need for restrictive security measures (e.g. surveillance) and the need to uphold civil liberties (e.g. privacy and freedom of speech). In responding to this dilemma, the article examines how this binary normative struggle impacts on the rhetorical presentation of counter-radicalisation policies – in particular, the UK Prevent Strategy and the rhetoric employed by UK Prime Minister and former Home Secretary, Theresa May. It argues that the normative environment has obliged May to construct rhetoric within the context of, what is termed here, normative invalidation. In facing two comparably compelling and related norms of action, May is necessarily required to invalidate or neutralise any norm not adhered to as an essential characteristic of rhetorical strategy. This is discussed in relation to the Strategic Narratives paradigm.