It is often argued that one of the desirable features of a democratic election is that every vote should be of equal value. One of the ways in which that principle can be realised is by ensuring that the ratio of representatives to voters is more or less the same everywhere.
In the case of Britain’s single member plurality system, that means ensuring that the number of voters in each constituency is more or less the same. If that is not the case, the votes of those in constituencies that contain fewer registered voters may be thought to have more weight and influence than the votes of those in seats with more voters. And if one party does especially well in constituencies with fewer voters, it is likely to secure what might be thought to be an unfair advantage in terms of its overall tally of seats.
At the last general election, there were some big discrepancies between constituencies in the number of registered voters that they contained. Leaving aside the island constituencies, where special geographical considerations may be thought to apply, there were on average just over 48,000 people to vote the ten smallest constituencies in the UK, but over 90,000 in the ten largest.
There are two main reasons why these discrepancies exist. First, until now, the rules for creating parliamentary constituencies have lacked any mechanism for equalising the sizes of constituencies across the four parts of the UK. Apart from a once and for all increase in Northern Ireland’s representation in 1983 and cut in Scotland’s in 2005, the number of constituencies in each part…