This article examines the commercial diplomacy between Britain and the People’s Republic of China during the 1970s and early 1980s, especially in relation to the British colony of Hong Kong. Recent historiography has focused on the negotiations over the transfer of Hong Kong’s sovereignty, agreed in 1984, and tends to argue that Hong Kong’s status as a colony was a hindrance to British attempts at improving relations with China during the 1970s and 1980s. Using two related case studies of British attempts to sell railway equipment to Hong Kong and China, this article addresses this debate before and in the immediate aftermath of China’s opening up in the late 1970s. It argues that whilst Hong Kong was a subsidised market for British-made rolling stock, its value as a ‘shop window’ for facilitating Sino-British trade was limited. Hong Kong was not a hindrance to British railway manufacturers exporting to China; but neither was it much of a help.