In 1942, 17 Leman Street, Whitechapel, was acquired by the Colonial Office and converted into the only seamen's hostel for black men in London. For seven years, this small government-sponsored hostel provided thirteen beds for seamen from British colonies in the Caribbean and West Africa. Considering the hostel amid wider contestations of nationhood in London’s built environment, this paper argues that the experience of ‘colonial’ seamen and stowaways in the capital was characterised by spatial precariousness, a condition accentuated by the unwillingness of authorities to respond to the difficult realities of the colour bar and citizenship in post-war urban space.