Crossing the floor: should we worry about MPs changing party?

By: Kathryn Wainfan

As MPs begin campaigning for the upcoming election, how should they interpret a vote in their favor? Is it merely a vote for their party’s platform, such that any coherent adult representing the same would win?  Alternatively, it might be that voters choose to support someone because of the candidate’s personal opinions and characteristics – “not his industry only, but his judgement”, as Edmund Burke put it in his speech to the electors of Bristol. Each interpretation brings different implications for how an MP should represent their constituents. 

If we assume that when voters cast their ballots purely based on party affiliation they do so because they believe that party’s platform is the best for them, it follows that an MP should stay in lock-step with their party’s platform, regardless of what they actually think is best for their constituents. This form of representation is known as a delegate model. In contrast, the trustee model says that an MP should vote against their constituents’ expressed opinions if the MP believes it will ultimately benefit their constituents more. Either model can lead to discontent.

In 1970 Albert Hirschmen outlined three options that members of an organization have in the face of the decreasing quality or benefits of an organization: exit, voice, and loyalty. In the case of MPs, staying loyal represents a form of the delegate model of representation by continuing to support their parties’ policies and hence what their constituents have voted for if we assume they voted for the party rather than the candidate. An MP using their voice exhibits more of a trustee style of representation by attempting to improve their party from the inside by expressing criticism or giving feedback. The final option is exit – leaving the party entirely. An MP choosing to exit their party by “crossing the floor” can be one of the most extreme manifestations of trustee representation.

Causes and Effects of Crossing the Floor

This year, before Parliament dissolved for the general election, two Conservative MPs willingly switched to the Labour Party – Dan Poulter on 27 April, quickly followed by Natalie Elphicke on 8 May. Both cited failures of the Conservative Party while in government as at least part of the motivation for their decisions. While Poulter and Elphicke’s defections garnered widespread attention and increased scrutiny on Rishi Sunak and the Conservative Party, crossing the floor remains very uncommon in the United Kingdom. Indeed, only 87 MPs have willingly left their parties since 1979. A further 115 have been forced to change their affiliations through either suspension from the House of Commons or removal of the party whip.

Of course, as with all political actions, party switching need not have noble goals. Parties may entice opposition legislators to switch by offering ministerial, committee, or other politically advantageous positions. Similarly, an MP may believe they will have better prospects for reelection running under a different party label (notably, however, neither Poulter nor Elphicke are seeking reelection). Researchers have found that MPs are more likely to cross the floor both when ministerial or committee positions are handed out and when closer to both sub-national and national elections. The prevalence of party switching varies widely across countries, and is more common in new democracies and democracies with more fluid party systems. 

The implications of MP party switching vary. At the most basic level, it can change the balance of power within a legislature. In countries where committee or cabinet positions are allocated based on seat share, gaining or losing MPs can alter a party’s ability to control agendas and set policies. At its most impactful, MPs crossing the floor can ensure a government survives or fails, as with Canada’s minority Liberal Government surviving a vote of no confidence in 2005.Extensive party switching can also create instability within a country’s party system, subsequently making it harder for voters to vote based on a party’s past performance or platforms. The inherent unpredictability associated with frequent party switching can also complicate day-to-day legislating. How can parties negotiate in good faith when it’s not clear that they will have enough MPs to accomplish what they’ve promised? There are also debates around the ethics of crossing the floor. On the one hand, MPs changing party affiliation to better serve their constituents may constitute a highly ethical decision, assuming an adherence to the trustee model of representation. However, MPs who do so for personal gain alone risk violating the bond between elector and elected. Regardless of which model of representation one favors, they both assume that voters cast their ballots based on who they believe will best look after their interests and that they can be removed at the next election following poor performance. The last point can be more challenging in electoral systems that only allow voters to select parties rather than individual candidates. 

Some countries have constitutional rules preventing MPs from crossing the floor, or requiring by-elections when they choose to do so – as of 2007, 41 countries had laws against legislators changing their party affiliations. In the UK, MPs tried twice to enact such legislation. In 2011 and 2022 MPs introduced Private Members Bills to require a by-election if MPs changed parties. However, as with most Private Members Bills, neither made it to a second reading. To date, there no British government has tried to create legislation to prohibit MPs from remaining in parliament after they cross the floor.

Laws against party switching are far more common in newer democracies and semi-democratic (sometimes called “illiberal democratic”) systems, though notably absent are any countries in western Europe. Proponents of these laws suggest that they prevent representatives from betraying their constituents by going against the platforms that voters endorsed. Scholars have also noted that these regulations can help stabilize a country’s party system. Voters can benefit from a more stable party system because party labels will provide more information about the values, political positions, and policies, which can in turn give voters more information with which to cast their vote.

Effects of Crossing the Floor in the UK

The electoral consequences of crossing the floor appear to vary across countries. Indeed, while many scholars and commentators praise the ideals Burke espoused in his Speech to the Electors of Bristol, fewer acknowledge that he lost his seat in the next election. Since 1979 83% of British MPs who willingly crossed the floor and ran for reelection lost their seats. 

Several features of the British parliament mitigate many of the concerns associated with MPs choosing to cross the floor. First, roll calls on significant issues in the House of Commons rarely rely on the support of only one or two MPs, particularly when it comes to passing final legislation, at least in the past 25 years. Thus, a few MPs changing their affiliation usually provides little threat to a government’s overall agenda. Additionally, the UK has a comparatively strong and established party system. The Conservative and Labour parties have dominated British politics for over one hundred years with only two other parties – the SNP and Liberal Democrats (and previously the SDP) gaining any significant representation. For the upcoming election, Reform UK is polling relatively strongly, but the UK’s first-past-the-post electoral system means that they are expected to gain few, if any, seats. Thus, some of the incentives for party switching in countries with fluid party systems do not apply and MPs crossing the floor pose little threat to the stability of UK’s party system. Finally, voters can directly punish or reward MPs who cross the floor should the choose to run for reelection. 

Ultimately, the main consequence of an MP crossing the floor comes from the publicity surrounding their decision to do so. Both of the recent defections away from the Conservatives garnered days of largely negative press attention for Sunak and his party, though Elphicke’s move also led to stories of disagreement within the Labour Party. While there is no doubt that party insiders would prefer to avoid such negative attention, public scrutiny is an important part of the democratic process. Overall, MP party switching poses very little threat to the day-to-day functioning of the government, nor the overall democratic nature of the British political system.  

Kathryn Wainfan.

Kathryn Wainfan holds a PhD in Political Science from the University of California, Los Angeles. She has been a lecturer in Political Science at the University of California, Los Angeles, University of California, Merced, and Loyola Marymount University. 

The Constitution Society is committed to the promotion of informed debate and is politically impartial. Any views expressed in this article are the personal views of the author and not those of The Constitution Society.