Labour's leadership candidates are mounting a last-minute bid to sign up supporters to vote for them amid continuing fears the contest could be skewed by "entryism".
As Jeremy Corbyn appeared to pull ahead in the race to succeed Ed Miliband, his rivals Andy Burnham, Yvette Cooper and Liz Kendall joined him in urging more supporters to register to vote ahead of the noon deadline.
A YouGov poll on Tuesday gave Mr Corbyn a commanding lead while bookmakers installed him as favourite, but the contest remains unpredictable due to a change in the Labour Party's rules for electing a leader.
Some 282,000 party members, 92,000 trade union and other affiliated members are eligible to vote, but members of the general public can also cast a ballot by joining Labour as a "registered supporter" for £3, with 70,000 so far signing up.
The rule change introduced by Mr Miliband has led to fears of entryism by hard-left groups or Tories seeking to influence the outcome of the contest, but the party has insisted it has robust procedures in place to identify them and stop their votes being cast.
The campaign teams of all four candidates attended a meeting yesterday designed to clear up confusion around how the competition would work, while Labour MP Simon Danczuk called for the contest to be re-run.
Despite the deadline to register as a member or supporter passing today, Labour insisted it would continue to weed out non-Labour supporters once ballots had been cast.
The process includes monitoring 20,000 social media feeds for people who have signed up as supporters but who may not back Labour.
Some 1,200 members or supporters of another party have already been excluded from voting in the leadership contest, including hundreds who had stood against Labour in local or national elections.
They included 214 from the Green Party, 37 from the Trade Unionist and Socialist Coalition, 13 Tories, seven from Ukip and one from the BNP.
Among those blocked include journalist and author Toby Young, film director Ken Loach, Tory MP Tim Loughton and Conservative peer Lord Callanan.
An unnamed former Liberal Democrat MEP signed up but was spotted by a Labour official while a group of Green Party supporters were found discussing ways around Labour's checks on a Facebook group.
But Labour has stressed that it is working to stop bogus supporters from influencing the contest, the result of which will be announced on September 12.
Meanwhile as Mr Corbyn appeared to be streaking ahead in the race, Ms Kendall made a pitch to the left of the party in an article for the socialist newspaper Morning Star.
The shadow care minister, seen as the most right-wing of the candidates, said she wanted to to "revive the Labour tradition of people power, taking us back to our party's roots in trade unions, co-operatives and mutuals".
She added: "I want to give voice to millions of people who see the changes they want to make in the world but feel powerless to do so. And I want to see workers having a far greater say over and stake in the companies they work for."