How people elect parliaments
The House of Commons is an assembly of (currently) 650 members. Numbers of seats are determined for each of the four ‘countries’ of the UK, which at present are 533 divisions for England, 40 for Wales, 59 for Scotland, and 18 for Northern Ireland. This allocation is not specifically proportional to population, and the total number of constituencies in each country is not fixed. Each country Boundary Commission (see below) has limited discretion to specify the final number of seats in its country. Overall, the present arrangements result in a significant measure of national malapportionment, noticeably favouring the degree of influence of electors in Wales and Scotland.
All members are directly elected in single member constituencies by the plurality voting method.
Under current legislation the boundaries of electoral divisions are drawn by independent Boundary Commissions for each of the four countries, operating separately. Boundaries are drawn so as to align with local government boundaries and also where possible to meet other non-partisan demographic criteria. Population numbers are used as a factor but are not a binding criteria. These Commissions conduct boundary reviews at least every 12 years. The proposals of the Commissions are subject to parliamentary approval, but may not be amended by the Parliament.
The most recent boundary review for Scotland was implemented prior to the 2005 election, while the other three countries had reviews approved in 2006 (Wales), 2007 (England) and 2008 (Northern Ireland), all of which were thus used for the 2010 general election. While these reviews are still relatively fresh, the malapportionment between the countries, together with the desire to align with local government boundaries, still results in a large measure of population (and thus voter influence) inequality across the UK as a whole.
Legislation debated in 2012 would have reduced the size of the House to 600 members, reallocated the numbers of seats between the 4 countries to remove malapportionment at the country level, mandated boundary reviews every 5 years, and required that the population of each constituency must be within 5% of the whole-of-UK average. This legislation would of course have triggered a new round of boundary reviews. The legislation was rejected in December 2012.
Inequality in the effective influence of voters caused by variations in House of Commons constituency enrolments has been fairly low in recent elections, with the standard deviation of variations compared to the mean enrolment being 12.3% in 2005 and 11.1% in 2010.
[nomination openness – party configurations]
[summary of results]
[inequality by divisions]
[inequality by margins]
2005 – 2010 – 2015 – 2017
[data source – data completeness – anomalous contests – augmentation]
[Datasets are not yet published]