ABSTRACT
This chapter examines the set of political parties in a political system, and their interactions in United Kingdom. The most familiar way of defining party systems is to look at the number of parties which have a realistic chance of participating in a government, rather than the number of organisations that nominate candidates at elections. In the case of the UK, the long-established idea of two-party competition has come under additional scrutiny since the introduction of devolved institutions in Scotland, Wales and Northern Ireland, elected by different varieties of proportional representation (PR). In fact, even when the national and regional variations are screened out, there is plenty of room for debate about the nature of the UK party system as it stood after the 2010 general election. The variations are most pronounced when authors compare the effective number of parties in general elections with the figures which arise from elections to the devolved assemblies in Scotland, Wales and Northern Ireland.
