Using a method for decomposing electoral bias in a three-party competitive system we contend that discussion surrounding electoral reform for the House of Commons is largely based on misconceptions about bias sources at recent British general elections (Northern Ireland is excluded from the analysis). Labour is the principal beneficiary across these seven elections while the third party, the Liberal Democrats, consistently suffers from a negative bias. There is no clear pattern for the Conservative party, however; it experienced a positive net bias at two of the elections but was disadvantaged for the remaining five. For three bias components – electorate, abstentions and minor party – Labour consistently has a positive advantage and the Conservatives are always disadvantaged. Abstentions contribute relatively strongly to Labour's advantage but differences in electorate size are not a major contributor to overall bias. Despite this, legislation changing the independent boundary review process is predicated on the assumption that new rules should remove much of the pro-Labour bias. The analysis finds instead that most bias stems from the geography component: differences in the distributions of each party's votes and the translation of votes into seats. Vote distribution is clearly the largest component explaining the Liberal Democrats' disadvantage but it is also the largest component for both Conservative and Labour parties in five of the last seven general elections. Although future boundary reviews will remove the effects of unequal electorates, this process is not designed to address either the impact of turnout/abstention or vote distributions on overall electoral bias.