The Labour party is set to appeal a High Court ruling allowing new members to vote in the upcoming leadership election between Jeremy Corbyn and Owen Smith. The decision on Monday (8 August) came after five Labour supporters accused the National Executive Committee (NEC) of improperly "freezing" them – and others – out of the contest, even though they had "paid their dues."

The appeal hearing is expected to take place on Thursday (11 August). A Labour spokesman said the party will appeal to "defend the NEC's right, as Labour's governing body, to uphold the rule book, including the use of freeze dates."

Last month the NEC ruled that those who did not have six months' continuous membership up until 12 July could not cast their vote. Those who joined after 12 January would only be allowed to vote if they paid an additional £25 ($32.56).

In his judgement, Mr Justice Hickinbottom said: "For the party to refuse to allow the claimants to vote in the current leadership election, because they have not been members since 12 January 2016, would be unlawful as in breach of contract."

Around 130,000 new members were affected by the freeze and the subsequent ruling. According to reports, most new recruits are believed to back Corbyn.

The Opposition leader welcomed the High Court decision at a campaign rally in Bristol. "The judge seemed very clear that his decision was all members of the party should have a right to vote in the leadership contest. Surely that has to be the right decision," he said.

Smith on the ruling to call for a prolonged leadership contest, which is due to end on 24 September. "Now many more members will have the chance to vote in the leadership election, I am today calling for an extension of the timetable so that all members have the opportunity to engage with Jeremy and me before making their choice," Smith said.

Shadow Chancellor John McDonnell – who supports Corbyn – slammed the decision to appeal the judgement and warned of a potentially large legal bill. "This is a deeply disappointing decision by a small clique of people behind closed doors, many of whom have openly expressed their opposition to Jeremy Corbyn's leadership, who are now trying to use Labour members' money to fund what they think is a further attack on Jeremy. However, this is just an attack on the basic democratic rights of members in our party," he said.

"We are a democratic socialist party, you cannot have one without the other. I hope that Labour HQ rethinks this decision as it could leave a legal bill in the hundreds of thousands of pounds that we could be spending instead on campaigning to hold this Tory government to account, instead of subverting our own democratic processes.

"Due to this decision, we are now in the absurd position that Labour HQ is wasting members' money to prevent members having a democratic vote on the leader of their choice, which has already been firmly upheld by a High Court judgement."

Taking a swipe at the infighting plaguing the Opposition, Conservative Party chairman, Sir Patrick McLoughlin, said: "This summer, the Labour Party have held more High Court battles than leadership hustings. At a time when the people of Britain look to a party who will fight for them and their family, Labour are spending their summer fighting amongst themselves."

The five claimants are Christine Evangelou, Rev Edward Leir, Hannah Fordham, Chris Granger and "FM", a new member under 18-years-old.