Ruling affects almost 130,000 party supporters who were impacted by the freeze
Five new UK Labour members have won a High Court battle over their legal right to vote in the forthcoming leadership election.
The members accused the party's National Executive Committee (NEC) of unlawfully "freezing" them and many others out of the contest between Jeremy Corbyn and Owen Smith even though they had "paid their dues".
The NEC decided that full members would not be able to vote if they had not had at least six months' continuous membership up to 12 July - the "freeze date".
But Mr Justice Hickinbottom ruled that refusing the five the vote "would be unlawful as in breach of contract".
The court action affects almost 130,000 Labour supporters who were impacted by the freeze.
It is unclear whether the ruling means these all of these supporters will now be able to vote in the contest.
A Labour spokesperson said: "It is right that the Labour Party seeks to defend vigorously decisions of the National Executive Committee in this matter, and we will now study this judgement carefully."
To gain the right to vote, members were given a window of opportunity, between 18 and 20 July, to become "registered supporters" upon payment of an additional fee of £25. Non-members were given the same opportunity.
The five who won the legal challenge are Christine Evangelou, Rev Edward Leir, Hannah Fordham, Chris Granger and "FM", a new member aged under 18.
The judge said that at the time each of them joined the party "it was the common understanding, as reflected in the rule book, that, if they joined the party prior to the election process commencing, as new members they would be entitled to vote in any leadership contest".
Mr Justice Hickinbottom added that that was the basis upon which the five joined Labour, and the basis of their contract with the party.
The judge overturned the requirement that they must have been members since 12 January - at least six months' continuous membership up to 12 July - the "freeze date".
He declared: "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."
Labour has been given permission to appeal to the Court of Appeal and it is understood the appeal could be heard later this week.