Parliamentary constituency boundary reviews and electoral bias: How important are variations in constituency size?

It is frequently canvassed by some politicians and political commentators that the current British electoral system is biased against the Conservative party because of variations in constituency size: seats won by the Conservatives at recent elections have been larger than those won by Labour in terms of their registered electorates, thereby disadvantaging the former. As a consequence, it is argued that equalisation of constituency electorates by the Boundary Commissions would remove that disadvantage. The validity of this argument is addressed in two ways. First, we demonstrate that the rules and procedures applied by the Boundary Commissions when redistributing seats in the UK preclude the achievement of substantial equality in constituency electorates. Secondly, we use a recent adaptation of a widely-used procedure for establishing electoral bias in three-party systems to show that variations in constituency electorates had only a minor impact on the outcome of elections after the last two redistributions. The geography of each party's support base is much more important, so changes in the redistribution procedure are unlikely to have a substantial impact and remove the significant disadvantage currently suffered by the Conservative party.