How Do MPs in Westminster Democracies Vote When Unconstrained by Party Discipline? A Comparison of Free Vote Patterns on Marriage Equality Legislation

The UK and Australian literature on free vote patterns highlights that, even under 'unwhipped' free vote circumstances, party membership remains the key predictor of MPs' voting patterns. However, analyses of free votes have focused on single parliaments and as such, it is not clear whether the insights of this literature can be generalised. This article analyses MPs' voting behaviour, during free voting on landmark legislation, which sought to allow equal marriage rights to same-sex couples in Australia, New Zealand and the UK. The article will address the following questions: Which MPs supported proposals to legalise same-sex marriage? What were the main factors that predicted their voting? Why were the majority of MPs in the UK and New Zealand, but not Australia, willing to support law reform? Whilst voting in the UK and New Zealand followed a strikingly similar pattern, there are key differences in the voting in Australia. This is attributed to two main factors: first, the 'whipping' of small 'l' liberal Coalition MPs in the Australian House of Representatives who might have otherwise voted in favour of reform; and, secondly, the different pathways along which the 'centre-left' political parties have evolved in New Zealand and Australia, which led to a larger presence of Catholics in the Australian Labor Party than in either the UK or NZ Labour Parties. It is possible to conclude from the analysis more broadly, that although party remains the best predictor of voting patterns across the three Westminster democracies recently, gender has also emerged as an important predictor of voting patterns. This finding is discussed in the final part of the article.