Labour has apologised after "technical issues" left people unable to sign up for a vote in its leadership election hours before the deadline to register.
Visitors to the party's website seeking to become a "registered supporter" were met with a series of error messages ahead of the midday cut-off to secure a voice in the contest.
"Apologies if you experienced problems trying to join or register as a supporter this morning. Our site is working now," it told would-be voters by Twitter.
The process has proved highly controversial, with a number of MPs calling for a re-run over allegations that it has been exploited by hard-left groups and political opponents including Conservative activists.
Demands for a "pause" have been fuelled by the surprise emergence of left-wing veteran Jeremy Corbyn as the favourite to succeed Ed Miliband.
A YouGov poll on Tuesday gave him a commanding lead while bookmakers installed him as favourite to see off the challenge of Andy Burnham, Yvette Cooper and Liz Kendall.
Some 282,000 party members, 92,000 trade union and other affiliated members are eligible to vote, but members of the general public can 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" but the party insists it has robust procedures to identify and stop such votes being cast.
Around 1,200 members or supporters of another party have already been excluded from voting in the leadership contest, including hundreds who 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.
Labour said the process of stopping bogus supporters from influencing the contest, the result of which will be announced on September 12, would continue once the deadline passed.
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 joined those calling for the contest to be re-run.