This chapter assesses British party policy (as expressed in general and European election manifestos) and public opinion (using Eurobarometer and British Social Attitudes data) towards deeper and flexible integration. The chapter begins by analysing policies and public opinion towards the speed of European integration and the nature of Britain’s EC/EU membership. Subsequent sections analyse party policies and public opinion regarding specific developments linked to deeper and flexible integration. The chapter analyses party and public attitudes towards opt-outs and enhanced cooperation—developments that allowed for differentiated integration within the EC/EU. Subsidiarity, a concept that sought to place limits on the EC/EU’s powers, is then analysed before the chapter concludes by investigating views towards decision-making within the EC/EU. The chapter argues that Conservative, Labour and Liberal policies towards these matters differed significantly from one another. Amid these party-political differences, public opinion towards the flexible institution British governments helped fashion was rather confused. In some circumstances, public preferences appeared to match those of the government and main parties. However, in notable areas they did not.