The UK Labour Party’s leadership election is underway, with a final decision due after a ballot of party members and affiliated supporters on April 4. Four candidates remain in the running, following an initial round of nominations by Labour MPs (and MEPs).

Under Labour’s system, the party’s MPs have relatively little control over the outcome, serving only to narrow the field before members make the final choice. A leader could therefore emerge who has little support from parliament – as happened in 2015, when Jeremy Corbyn was elected. This arrangement departs significantly from the original basis for choosing UK party leaders and has potentially destabilising effects on the whole political system, given parliament’s centrality.

Traditionally, MPs chose party leaders. Labour was the first party to diverge from this. Under pressure from left-wing activists, who believed MPs were prone to picking overly centrist leaders, Labour agreed to give greater say to local parties and trade unions. It adopted the so-called “electoral college” in 1981, giving equal weight in the final outcome to three groups – MPs, constituency parties and affiliated organisations. MPs continued to control the initial nominations.

This system survived largely intact for decades without upset. The final ballot outcome was consistent with MPs’ own preferences for the elections of Neil Kinnock in 1983, John Smith in 1992 and Tony Blair in 1994 (while Gordon Brown’s 2007 succession was uncontested).

Cracks began showing in 2010, when Ed Miliband was elected despite his brother David having greater support from both MPs and party members. To avoid future splits in the electoral college, Ed Miliband abolished it. He gave the final say to members, registered supporters and affiliated members, who all participate on an equal basis. This system elected Corbyn and is being repeated (with minor modifications) now.

The Conservative Party changed its rules more slowly and retained more safeguards. Famously, Conservatives used to pick their leader through a system of informal “soundings” in the parliamentary party. Formal elections, which were still among MPs only, weren’t introduced until 1965.

William Hague brought in a new system in 1997. This echoed Labour’s by including the wider membership, but it retained stronger parliamentary party control. MPs vote in a series of ballots (if necessary) to choose two candidates. Members then vote on these finalists. But in 2003 and 2016 the parliamentary party agreed on a single candidate (Michael Howard and Theresa May, respectively) without a member ballot.

Parliamentary accountability

The emphasis on members in these elections has weakened traditional lines of accountability. Although MPs (very narrowly) put Corbyn on the ballot in 2015, for example, it was always clear that only a minority supported him. In 2016 he suffered a vote of no-confidence among his MPs when 172 (81%) voted against him and only 40 in favour. Despite this he won a fresh leadership contest among members, leaving Labour MPs with a leader they plainly did not support.

This situation is constitutionally problematic. The UK is a parliamentary democracy, meaning that the government (and by association its leader) must retain the confidence of the House of Commons to remain in office. A UK party leader is chosen as a potential prime minister, but can only govern successfully if they have parliament’s support.

A leader lacking their own party’s confidence is simply not credible as prime minister – a fundamental point recently recognised by former Labour Deputy Leader Tom Watson, who commented: “as soon as the leader loses the confidence of the parliamentary party it’s almost impossible to see how you can form a government”.

Iain Duncan Smith’s election as Conservative leader in 2001 has some echoes of the Corbyn case. Michael Portillo, the original frontrunner among MPs, was knocked out through strategic (and perhaps partly miscalculated) voting. One participant suggested that some MPs “were making a statement by voting for Duncan Smith but didn’t really expect him to become leader as a result”.

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An analysis of his leadership later suggested that his legitimacy was significantly undermined by a lack of endorsement from the parliamentary party. Duncan Smith was ultimately ousted before he could face the electorate, leading to Howard’s uncontested elevation to leader in 2003.

What should be done?

If membership ballots undermine parliamentary accountability, weaken parliamentary parties and cast leaders’ legitimacy into doubt, what can be done, and most pressingly, what can be done in the Labour contest currently underway?

Long term, a thorough review of leadership rules seems warranted. This includes thinking about how many MP nominations a candidate should need to get on the ballot and whether people should be allowed to register with the party just to cast a vote in the leadership election. More than 100,000 people have joined Labour since December – which at one level seems healthy, but also raises concerns about infiltration (which clearly occurred to some extent in 2015).

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A compromise would be for Labour to adopt something closer to the Conservative rules, giving a larger role to the parliamentary party. But the Duncan Smith case shows that these have problems too.

A more radical approach would be to accept the logic of a parliamentary system, and return the choice of parliamentary leader to MPs. They, after all, know the candidates best, and can also decide quickly – as the Conservatives did in 2003 and 2016.

Shorter term, if Labour’s new leader is to succeed, it seems essential that they have the confidence of the parliamentary party. Emily Thornberry (who received the smallest number of MP nominations) has pledged to step aside if she lacks that confidence. As a minimum, other candidates should promise the same. The Conservative Party rules already prevent a leader who has lost the parliamentary party’s confidence from standing again. Such a rule seems a minimum requirement to ensure the integrity of the system.