One of the salient characteristics of the British first-past-the-post electoral system is the amount of bias which it produces. Parties with large percentages of the votes (i.e. 25 or greater) almost invariably get even larger percentage shares of the parliamentary seats, whereas those with smaller vote percentages tend to get very few seats. That bias largely reflects the superimposition of a geography of constituency boundaries on the geographies of party support, so that different sets of constituencies can produce different levels and even directions of bias, as is clearly illustrated in studies using US data.See, for example, R. L. Morrill, ‘Ideal and Reality in Reapportionment’, Annals of the Association of American Geographers, 63 (1973), 463–77. More generally on bias in electoral systems, see D. W. Rae, The Political Consequences of Electoral Laws, 2nd edn (New Haven, Conn.: Yale University Press, 1971); and R. Taagepera and M. S. Shugart, Seats and Votes: The Effects and Determinants of Electoral Systems (New Haven, Conn.: Yale University Press, 1989).