Labour electoral landslides and the changing efficiency of voting distributions

The translation of votes into seats under first-past-the-post electoral systems with single-member constituencies invariably results in disproportional allocations of seats relative to votes among the main two parties. It also tends to produce biased outcomes, with one party getting a more disproportionate share of the seats with a given share of the votes than does its opponent. In Great Britain, these biases favoured the Conservative party until the 1980s, but now strongly favour Labour. Production of those biases results from a variety of influences involving the interaction of the geography of party support with that of constituency boundaries. Increasingly, that interaction has favoured Labour: without any explicit manipulation of the constituency map to its own ends, it now benefits substantially from the equivalent of the malapportionment and gerrymandering cartographic abuses typical of the United States, because of its ability to manipulate its vote distribution within the constituency system.