Abstract
This article examines the legal implications of the United Kingdom’s shift in nuclear deterrent strategy in the early 1980s from population to leadership targeting. Drawing on the 1978 Duff–Mason report, a government study evaluating options for deterring the Soviet Union, as well as other archival sources and open-source data, we construct representative population and leadership target sets and estimate the resulting civilian fatalities using nuclear-weapon-effect simulation tools. We find that UK strikes against Soviet leadership targets would have caused three to ten million civilian deaths—compared to 13 million from a population attack—while rendering large areas uninhabitable for decades. Although UK officials claimed that counter-leadership targeting was ethical because civilians were not deliberate targets, the scale of civilian harm undermines this assertion. The historical record reveals that officials considered such casualties necessary for deterrence, casting doubt on the legality of this strategy. Extending our analysis to contemporary Russia and the current UK arsenal confirms that these findings remain valid.