Newly elected leader of Britain’s opposition Labour party Jeremy Corbyn leaves the party’s headquarters in London on Sept. 14. (Justin Tallis/AFP/Getty Images)

Jeremy Corbyn’s election as leader of Britain’s Labour Party — despite the opposition of Tony Blair, Gordon Brown and most of Labour’s elite — is a major shock to Britain’s political system. It has been clear for several weeks that Corbyn was likely to win. Yet when he decided to run for leadership, he was regarded by political commentators as a complete outsider. His success suggests that there’s something wrong with Britain’s pundits — and perhaps with Britain’s party system.

In 2013, Peter Mair’s book “Ruling the Void” came out, two years after the author had died unexpectedly of a heart attack. Obviously, Mair didn’t predict the rise of Jeremy Corbyn in particular. Nonetheless, his diagnosis explains why someone like Corbyn could succeed, against the odds, and gives us some sense of his chances for success in future.

There’s something rotten in Britain’s and Europe’s political parties

Mair’s book is a study of European political parties — and how they no longer play the role that they are supposed to. Once upon a time, political parties like Labour created a vital link between the public and political decision making. They were never perfect, but they allowed citizens to get involved in politics, and, when they didn’t like what the government was doing, to vote against the parties that run it.

Now, this is no longer true. Mair argues that a twofold process is taking place. First, European political elites — the people who really make decisions — are finding that they don’t really need the party rank and file as much as they needed. Parties are supported more by state funding than by members. Party leaders are more interested in their role as part of the government than in representing their voters. Second, the ordinary public is drifting away from parties. They are less likely to vote, and when they do vote, they are more likely to shift from party to party.

Mair argues that this is bad for democracy. Quoting another political scientist, Rudy Andeweg, who says that “the party … becomes the government’s representative in the society rather than the society’s bridgehead in the state,” Mair suggests that political parties are becoming glorified spin doctors for state power. The structures of power and decision making are increasingly “protected from the people and from excessive input.” As  British sociologist Colin Crouch argues, this also means that political elites come to identify less and less with voters, and more and more with the representatives of special interests whom they socialize with, who provide them with financial support, and who shape their fundamental ideas about what policies are acceptable and what policies are unacceptable.

This describes the evolution of Britain’s Labour Party

The Labour Party used to be as much a social movement as a party, with mass membership and a strong relationship with the unions. It hasn’t been that for decades. Successive Labour leaders have sought to weaken the role of ordinary members and the relationship with unions. Mair talks about how Gordon Brown, the previous leader of Labour, rejected a proposal that had just won the support of a large majority at the Labour party conference, saying, “It is for the country to judge, it is not for a few composite motions [at party conference] to decide the policy of this government and this country. It is for the whole community and I’m listening to the whole community.” This is emblematic of a wider shift. Labour’s leaders have become part of Britain’s political elite, well integrated with the state, and relatively friendly to the financial sector (which arguably is even more politically influential in the U.K. than in the U.S.). Labour’s mass membership — like the membership of other European political parties, has dwindled, as voters have become more apathetic.

Corbyn’s election has challenged this tendency

As part of Labour’s reform plans, it replaced its old system for electing leaders (in which one third of the votes were cast by members of Labour’s parliamentary party, one third by ordinary members and one third by unions and other affiliated organizations) with a simpler system, under which the parliamentary party nominated potential candidates (to compete, a candidate had to have the support of 15 percent of the parliamentary party) but ordinary Labour party members and ‘registered supporters’ of the Labour party voted on which candidate would become the leader.

This was intended both to encourage people to join Labour and to weaken the unions. It didn’t turn out that way. Jeremy Corbyn was nominated by a sufficient number of Labour MPs, including some who didn’t actually support him, but wanted to ensure that Labour’s left wing didn’t feel excluded. However, it turned out that he had far more supporters than Labour’s elite expected.

Some of these were union members — even if unions didn’t have an automatic third of the vote any more, several could and did encourage their members to become Labour party members and to vote for Corbyn. Some of the active unions had disaffiliated themselves from the Labour party (which they saw as insufficiently protective of their interests), but their members were still able to join the Labour party as individual supporters and vote. Other people joined the Labour party to vote for Corbyn, thanks in part to a widespread social media campaign.

While there isn’t any good research yet, it’s likely that many of these were people who were unhappy with Britain’s austerity politics, and wanted to push Labour to oppose austerity more directly. The result was that Corbyn won by an enormous margin, getting nearly 60 percent of the vote in a four-way race. In Mair’s terms, he succeeded because the Labour party had become disconnected from its base of supporters, discrediting its leaders.

The Labour party still faces an uncertain future

The election has seen a massive increase in the number of Labour party members and registered supporters, thanks to Corbyn’s supporters flooding into the new system. It has also seen continued growth after Corbyn’s election as party leader.

This would seem to suggest that Corbyn’s rise shows parties how to reverse the trends of recent decades — if they want to. However, the situation isn’t nearly as clear cut as that. The old mass membership parties of the early 20th century were based on social institutions that no longer exist. Being a member of the Labour party wasn’t just about voting for leader — it was about identity and social life. It was also rooted in a U.K. industrial economy that has dwindled in the last few decades, even in its stronghold in Northern England. Unions are far weaker than they once were, except in the public sector. Finally, Labour was a U.K.-wide phenomenon — the Labour party was strong everywhere in Britain except in Northern Ireland (where it had reliable allies in the Catholic Social Democratic and Labour Party). Labour has now lost Scotland, weakening it substantially.

It’s not at all clear that the new forms of collective identity which have helped propel Jeremy Corbyn to leadership will be anywhere near as enduring as the old ones. Perhaps the new party base will help recreate a mass membership party connected to its leadership. But perhaps also not. Even if party membership has grown, it is still nowhere near what it was in Labour’s days of strength.

What is clear is that Corbyn’s Labour party will face relentless opposition from the elites that have replaced the masses as the main source of resources for parties and politicians. U.K. businesses — and especially the financial elite of London’s city — are vehemently opposed to Corbyn’s leadership and political project, which potentially destabilizes a the consensus that they see as essential to Britain’s and their own prosperity.

If Mair is right — and parties have become increasingly disconnected from their base of support — then Corbyn’s election may be seen as a way of trying to revitalize this connection. The problem is twofold. It isn’t clear that the base for mass parties is there as it used to be, but it is is clear that the elites whom parties have come to depend on like the system the way that it is, and have resources that they will use to protect it. Corbyn likely isn’t the leader that the Labour left would have chosen, if it had thought it had a real prospect of success (and indeed he was in part chosen by the people who now oppose him). More importantly, perhaps, it’s not clear that the social and political conditions which once allowed people like Corbyn to succeed are there any more.