A number of elements within a voting system can contribute to electoral bias (i.e. when two or more parties obtain similar levels of voter support but receive significantly different shares of parliamentary seats). Such elements include:
1. Unequal electorate size (mal-apportionment)
2. Voter distribution (geography)
3. Different levels of turnout (abstention or under-registration).
4. Competition from smaller parties
The current UK electoral system favours the Labour party (worth 63 seats at the last election) and the Coalition government sees an urgent need for new parliamentary constituency boundaries to remove the advantage Labour is perceived to gain from unequal electorate size (1. above). The Conservatives prefer a House of Commons reduced to 600 seats (-7.7%) – a smaller Commons also saving taxpayer money – and a single electoral quota of around 76,000 electors per constituency.
However, Colin Rallings and Michael Thrasher, directors of The Elections Centre, University of Plymouth, consider that the effect of such mal-apportionment (1. above) on the Labour advantage is much less than the way in which the Labour vote is more efficiently distributed (2. above) across the Country, turnout (3. above) in Labour seats also being lower. Labour is, therefore, accusing the Coalition of trying to fix constituency boundaries for political purposes and pointing out that of the around 3.5 million UK residents qualifying for a parliamentary vote but missing from electoral registers, very many are in Labour ?supporting areas, one reason why Labour MPs represent smaller constituencies on average.
In a reduced Commons, Labour could lose 27 (11%) of its current 258 seats, the Liberal Democrats 6 (11%) of their 57 seats and the Conservatives 13 (4%) of their 307 seats, the latter then still short of an overall majority (of 301 seats out of 600) despite being well ahead of Labour in the popular vote. It should be noted, however, that although the boundary review will solve the problem of mal-apportionment (1.), ignoring the bias produced by the other important elements (2. and 3. above) may result in Labour only losing around 10 ? 12 % (i.e. – 27 + 13 + 6 seats) out of its total advantage of 63 seats.