Voting in the Labour leadership election is set to close at midday - despite claims many members have still not received their ballot papers.
Hopefuls Andy Burnham, Jeremy Corbyn, Yvette Cooper and Liz Kendall will learn who has won the contest at a special conference on Saturday.
Corbyn, the left-wing veteran MP for Islington, is odds on favourite to win.
The party has been plagued by internal rows through the contest amid concerns non-Labour supporters have been able to infiltrate the process by registering to vote.
As late as yesterday, party members were still taking to Twitter to voice their frustration at not receiving ballot papers.
Andy Burnham's campaign manager Michael Dugher criticised the party for closing a call centre that was helping members trying to vote.
Corbyn - who initially struggled to win a place on the ballot - has gone from rank outsider to the surprise favourite in the contest, with thousands attending his rallies over the last few weeks.
But his rise to prominence has been met with warnings from Labour figures past and present that the party is in danger of "annihilation" if he wins.
Despite suggestions that no other candidate could match Corbyn's surge in support, the contest could still throw up a surprise.
Under the voting system, if no contender achieves 50% of the vote in the first round of counting, second preference votes come into play which could allow Andy Burnham or Yvette Cooper to take the top job.