BRITAIN’S opposition Labour Party will announce the result of its leadership election on September 12th. Both the polls and the betting odds suggest that Jeremy Corbyn, a veteran of Labour’s far left and a record-breaking opponent of his own party in parliament, will win. That threatens a damaging row. Only 20% or so of Labour MPs are thought to want Mr Corbyn as leader. Having lost badly earlier this year under an unpopular, leftish leader, Ed Miliband, they are united in not wanting to repeat the mistake. So how did he become the frontrunner? Mr Corbyn’s path so far has been smoothed by a series of accidents. He entered the race at the last minute, scraping half of his 36 nominations from fellow MPs who had said they would not themselves vote for him, but were uninspired by the rest of the field and wanted a more lively “conversation” among the party. Unexpectedly, that conversation turned out to be almost exclusively about Mr Corbyn, who surged ahead among the wider party “selectorate” of party and union members. That is one accident. Another is that, as a result of new election rules introduced last year, MPs are now largely powerless to stop him. The new system abolished Labour’s electoral college, whereby three groups—MPs, unions and party members—all counted in equal measure towards the final result (see chart). This time, all votes are counted individually, which means the MPs’ votes are just 232 among some 550,000 in total. Nomination being the only power MPs still have, using it to nominate Mr Corbyn now seems especially frivolous.

Meanwhile, this dilution of MPs’ power was accompanied by a record surge of new members. This too has helped Mr Corbyn. A YouGov poll conducted last month found a majority backing him among every group, save those members who joined the party before this year’s election (40% of whom backed him). Most conspicuous among the recent influx is a new type of voter, the “registered supporter”. Inspired by the French Socialists’ 2011 primary, which enlisted millions of new voters all paying a few euros each, Labour decided to follow suit. These "three pound" members, despite signing up in similar numbers to union and party members, have caused some embarrassment. Troublemakers from other parties, encouraged by politically conservative journalists, have tried to join with the aim of consigning Labour to the electoral wilderness—by ensuring a victory for Mr Corbyn. The party was then accused of conducting a "purge", after it excluded not only members of rival parties but also left-wing groups from Labour’s fractious past (mainly it expunged voters not on the electoral register).

When Labour’s fortunes were revived under Tony Blair, who become leader in 1994 under a system which abolished block votes for union and party bosses (and who supported the recent reform), it seemed to many that the party would be sure to win more elections as it became more democratic. The logic of Labour’s optimistic years may have been valid, but not for ever. In any case, should Mr Corbyn win the leadership, the rest of his party will face a struggle to evict him. Labour’s rules require it to wait a year before a vote of no confidence, after which another full election will have to take place.