Following Prime Minister Theresa May’s statement of 12 March 2018 in response to the Novichok incident in Salisbury, news reports and social media platforms were awash with talk that it constituted an armed attack by Russia against the UK, that the UK had a right to respond in self-defence, and even that an international armed conflict existed between the UK and Russia. The circumstances of the incident and the response of the UK government raise important questions of international law. Stephen Lewis considers whether the Salisbury incident, assuming it was carried out by Russia, amounts to an ‘armed attack’ for the purposes of Article 51 of the UN Charter, engaging the UK’s right to forcible measures in self-defence, and explores the potential legal consequences of characterising the incident as a use of force.