Labour’s leadership election could be delayed after a court ruled an extra 130,000 people should be given a vote.

The decision would almost certainly hand victory to the current leader Jeremy Corbyn.

Within hours Labour announced that it would appeal against the High Court ruling, while Mr Corbyn’s rival Owen Smith called for the contest to be extended.

A delay in the vote would leave the party’s annual conference in Liverpool in September dominated by the leadership question.

Meanwhile, a new report suggested that Labour’s woes and the ongoing review of Westminster constituency boundaries could hand the Conservatives a 90-seat majority in the Commons.

A poll last week shoeing the Conservatives 14 percentage points ahead of Labour prompted speculation of a snap general election.

Labour was thrown into chaos when judges rejected the party's decision to bar those who joined after January from voting in the leadership contest.

The court ruled in favour of five supporters who accused Labour's National Executive Committee (NEC) of unlawfully "freezing" them out, even though they had "paid their dues"

Party officials said Labour would mount a legal challenge, “to uphold the rule book, including the use of freeze dates".

The appeal is due to be heard on Thursday, just hours before Mr Corbyn and Mr Smith go head-to-head at a hustings in Gateshead.

If upheld, the ruling is expected to be a massive boost to Mr Corbyn's fight to keep his job.

Most of those who have signed up since the beginning of the year are believed to support the veteran socialist.

Earlier, Mr Corbyn's allies had urged the party not to appeal the judgement.

John McDonnell, the shadow chancellor and chairman of Mr Corbyn's leadership campaign, described the court decision as a "huge victory for Labour Party members and party democracy".

He urged Mr Smith to join Mr Corbyn to call on the party to rule out a legal challenge.

"I'm calling on Owen Smith to join with us in backing party members and calling on the Labour Party not to appeal and attempt to disenfranchise members."

"We are now calling on the Labour Party bureaucracy to act sensibly and play by the rules for the rest of this leadership election," he said.

Bookies slashed odds on Mr Corbyn winning from 1/10 to 1/16 after the ruling.

But Mr Smith insisted it was still " possible" he could win and described Mr Corbyn as “useless” during at a campaign event in Newcastle.

Before the decision Labour MP David Lammy warned that the party was in danger of splitting.

Most Labour MPs voted against Mr Corbyn in a confidence motion last month.

Dozens have also walked out of his shadow cabinet, leaving some Labour MPs forced to ‘double job’ on the frontbench.

But Mr Corbyn has refused to stand down, saying that the choice of leader was one for members not MPs.

At the weekend he suggested that he may not resign even if Labour loses the next general election.

Mr Smith said that an extension was needed “so that all members have the opportunity to engage with Jeremy and me before making their choice.”

Sources said that there was no timetable in mind but that an extra month could allow both candidates to reach out to new voters.

Meanwhile, a new report from the website Electoral Calculus estimates that the planned boundary changes alone would increase the Tory majority to 48.

Theresa May’s government party is currently well ahead of Labour in the polls, but has a majority of just 12 MPs in the Commons.

The Boundary Commission is currently considering how to shrink the number of MPs from 650 to 600.

A reduction in the number of seats in Scotland and Wales is expected to favour the Tories, along with a population shift towards southern areas where the party has strong support.