A quarter of people who signed up to vote in Labour's leadership contest are being investigated by the party

Most surviving sign-ups are believed to be supportive of Jeremy Corbyn

Jeremy Corbyn greets supporters at a rally in Liverpool's George Square (Getty)

Around a quarter of people who signed up to vote in Labour’s leadership election at the last minute have been flagged for investigation by the party, new figures suggest.

The Huffington Post UK reports that around 40,000 of the 183,000 people who paid £25 to sign up as a “registered supporter” have either already been excluded or are being examined by the party’s compliance team.

Labour has tightly restricted signups compared to last year’s leadership election – opening only a 48-hour window for signups and raising the fee from £3.

Despite this huge numbers of people signed up to vote, raising an estimated £4.6 million for the party’s coffers during the short period.

The most common reasons for rejections are having previously formally supported another political party, not being on the electoral register, or their payments bouncing, the website reports.

General Secretary Iain McNichol said last month that the party would also block people who sent abusive messages during the contest. It set up an email address to report people to.

The party has already collated a centralised list of people who are blocked from voting in the leadership election, but will spend another few weeks analysing submissions.

Sampling of the applications is believed to suggest the remaining sign-ups are largely supporters of embattled leader Jeremy Corbyn, by about 65 per cent to 35 per cent.

When people sign up to Labour they are asked to give a stated reason, though they are not explicitly asked which candidate they support.

The surviving registered supporters will be able to vote in the leadership contest on a par with members who signed up before January 2016, with tens of thousands of further trade union affiliates also expected to join.

In 2015 Mr Corbyn won with all categories of members – including full members, union or society affiliates, and registered supporters.

Polls conducted at the start of the campaign suggest he still has a significant lead over his rival Owen Smith, who is challenging him for the leadership. The incumbent has also been drawing significantly larger crowds to rallies during the campaign.

The pair’s first head-to-head leadership hustings will take place in Cardiff on Thursday. The final result will be announced just before the party’s conference in Liverpool in the autumn.