In 1958, Britain and Denmark both advocated closer European cooperation through the looser framework of the Free Trade Area (FTA) rather than membership of the nascent European Economic Community (EEC). By 1972, however, the situation had changed drastically. The FTA was a long-forgotten concept. Its replacement, the European Free Trade Association (EFTA), was deemed economically and politically inept. Now, at the third time of asking, both countries were on the verge of joining the EEC as full members. This book offers a compelling comparative analysis of how the European policies of the British Labour Party and the Danish Social Democrats (SD) evolved amid this environment. Based on material from twelve archives in four countries, it updates our knowledge of how the parties reacted to key moments in the integration process, including the formative stages of the EEC in 1958–60 and the negotiations for British and Danish EEC membership in 1961–63, 1967 and 1970–72. More innovatively, this book argues that, amid an array of national and international constraints, the reciprocal influence exerted by Labour and the SD on each other via informal party contacts was itself a crucial determinant in their European policymaking. In so doing, this work sheds light on the sources of Labour European thinking, the role of small states like Denmark in the European integration process, and the place of Anglo-Scandinavian relations in the broader story of contemporary British foreign policy.