Electoral bias at the 2010 General Election: Evaluating its extent in a three-party system

The three‐party method for bias decomposition shows that after the 2010 general election Labour continues to benefit from a positive bias but that its advantage over the Conservative party has diminished. Indeed, there is now a positive bias towards the Conservatives also while the position of the Liberal Democrats has deteriorated. The Parliamentary Voting System and Constituencies Act 2011 will change the boundary review process. This feature of the legislation is based on a view that Labour’s advantage relates to inequalities in electorate size which previous boundary reviews, constrained by existing rules, could not remove. However, close examination of the 2010 result shows clearly that most bias follows from the parties’ vote distribution and to a lesser extent electoral abstention. It follows that inequality in the size of constituency electorates, malapportionment, accounts for a rather small proportion of the overall bias. The boundary review, due to complete in 2013, will not, therefore, entirely remove Labour’s relative bias advantage over the Conservatives although both parties will continue to have a considerable advantage over the third‐placed Liberal Democrats.