This article examines the response of the British government to the revolution in Zanzibar in January 1964. It demonstrates that, once the safety of British nationals had been assured, British concerns centred upon the possibility that the new regime might become susceptible to communist influence. These fears appeared to be realised as British influence in Zanzibar diminished and the new government welcomed communist aid and advisers. In the aftermath of successful military interventions in support of moderate regimes in Kenya, Uganda and Tanganyika, and under pressure from Washington to take decisive action, the British prepared a series of plans for military action in Zanzibar. None of these was enacted and the final plan was scrapped in December. The paper examines the range of factors that undermined British diplomacy and inhibited the government from taking military action in Zanzibar. In doing so it illustrates the complexity of Britain's relationship with postcolonial regimes in East Africa and the difficulties that it faced when trying to exert influence in a region recognised by both London and Washington as a British sphere of influence.