The underlying purpose of this chapter is to demonstrate that the country’s electoral marketplace is more open than it once was and that, consequently, the competition for votes between parties is also more extensive. We begin with a consideration of how the electoral marketplace came to be relatively ‘closed’ in the first place, which entails an account of the historically derived linkages between parties and social groups in Britain, as well as the social psychology of fixed political identities. Following this, we examine how the electoral market began to open up after 1970, through a review of the widespread evidence of growing electoral instability since then. In truth, there never was an entirely closed electoral market in the UK, but since 1970 the evidence of significant electoral change suggests that the scope of competition has increased in line with an expansion of the market for ‘available’ votes.