Several campaign teams for leader and deputy say that many people are still waiting

Labour is under pressure to step up its efforts to ensure party members receive their leadership ballots amid widespread reports of glitches.

Several leadership and deputy leadership campaigns have told the Guardian their canvassers are picking up a large volume of party members still awaiting their ballot.

Q&A How does the Labour leadership contest work? Show Hide The first stage of the contest was for potential contenders to get the backing of 22 fellow MPs by 13 January. Five MPs passed this threshold: Keir Starmer (88 nominations), Rebecca Long-Bailey (33), Lisa Nandy (31), Jess Phillips (23) and Emily Thornberry (23). The second stage required each contender to win the support either of 33 constituency Labour parties (CLPs); or of three affiliates, two of which had to be unions, and which between them accounted for at least 5% of the affiliated membership. This had to be achieved before 14 February. Jess Phillips withdrew from the contest on 21 January. Emily Thornberry failed to attract the required number of members. The ballot of members and registered supporters was due to open on 21 February, and closes at noon on 2 April. To be eligible to vote you must have been a Labour member on 20 January, or have applied to have become a £25 registered supporter by 16 January. Corbyn’s successor - Starmer, Long-Bailey or Nandy - will be announced at a special conference in London on 4 April.

The issue appears to be particularly acute for new members who joined the party after December’s election, believed to number more than 100,000, who are being subjected to a verification process that involves checking their address against the electoral roll.

Polling suggests this group, as well as those who joined before Jeremy Corbyn became leader, are less likely to support his preferred candidate, Rebecca Long-Bailey.

Some may have joined in the hope of voting for Jess Phillips, who was campaigning for new members to sign up, but withdrew from the contest as it became clear she was unlikely to receive the endorsement of any of the major unions.

The latest YouGov poll showed 67% of members joining since the election backed Keir Starmer – against 43% who joined in the previous four years.

A source at one of the campaigns said: “It’s a small sample, but our phone-banking data is showing 80% of those who haven’t had their ballot paper joined either pre-2015 or post-2019 general election.”

A second campaign described a “large scale failure”, with “many, many people” having to reapply for their ballots.

Another Labour source, with knowledge of the process, claimed queries had been raised about the eligibility of thousands of new members, with staff unable to match their details with the electoral roll. Members are then contacted, and given the opportunity to resolve the discrepancy.

Labour’s website warns members they may have to wait up to 10 days for a ballot to be reissued if they have missed out. Members can also use a self-service portal to make the request, but there are claims of a backlog.

Chris Matheson, the MP for Chester and a Starmer supporter, said: “It is very worrying that two thirds of the way into this contest many Labour members appear not to have received their ballot papers. The general secretary needs to provide urgent assurance that all outstanding ballots will be dispatched as soon as possible.”

Lisa Nandy supporter Louise Haigh, the MP for Sheffield Heeley, said: “Lots of new members who have joined our party since the devastation of the general election to have a say in our future have a right to their vote and it must be exercised. The party need to sort this out immediately and make sure all members are reassured they will get a chance to vote.”

Voting opened last week, and will continue until noon on 2 April, with the result due to be announced at a special conference on 4 April. Labour officials declined to comment, but pointed out there is still plenty of time for queries to be resolved and ballots issued.

If none of the three remaining candidates win more than 50% of the vote in the first round, the third-place candidate will be eliminated, and their votes reallocated to those members’ second choice.

Long-Bailey has sought to shake up the race in recent days by challenging Starmer over how his well-oiled campaign machine is being funded.

Pressed on the issue by Andrew Neil on Wednesday, the shadow Brexit secretary revealed that the £100,000 donation from a fellow barrister he reported earlier this week was the largest he has received.

Long-Bailey told Neil: “I think there’s always an assumption that you don’t get something for nothing in this world. And those who donate to your campaign will expect to be repaid in some way in the future.”

Her campaign has received significant contributions from the Unite trade union, and from leftwing Labour group Momentum, whose founder, Jon Lansman, is chairing her campaign.

Wigan MP Nandy, who has been more critical of Labour’s policies and approach than either of her two rivals, told HuffPost on Wednesday she remained confident she could still win, saying there were “a lot of members who are undecideds, who haven’t made up their mind who their first choice is”.

She hopes to nose ahead of Long-Bailey, whose second preferences she would then hope to pick up.

There have been few stark policy disagreements during the campaign, with Starmer adopting 10 markedly leftwing “pledges”, including widespread nationalisation, abolishing tuition fees and passing a new law to prevent illegal wars.

Starmer received the backing of former Labour prime minister Gordon Brown on Thursday, who said he, “has all the qualifications that are necessary for a prime minister of the future”.

“A vote for Keir Starmer is a vote for hope. It’s a vote for the future. It’s a vote for the values that all of us believe in deeply,” Brown said.

Long-Bailey has prioritised the environment, saying she would seek to make it a part of Labour’s constitution, in a new clause IV. And she has also focused on party democracy, calling for open selection of all parliamentary candidates.