The Labour leadership contest should be extended by two extra weeks because more than 100,000 people could be added to the electorate, Owen Smith's campaign chief has argued.

Kate Green MP urged Labour's general secretary, Iain McNicol, to make the move after a High Court ruled against a decision from the National Executive Committee to block new members who joined Labour after 12 January from having a say in the election unless they paid £25 ($32).

"Giving some members as little as a week between confirming their vote and ballot papers landing is not sufficient time for them to gather the information they will wish to have about the candidates before they cast their vote," Green warned.

The call comes as Labour go to the Court of Appeal today (11 August) in a bid to reverse the High Court's decision. The appeal enraged shadow chancellor John McDonnell, Jeremy Corbyn's campaign chief.

"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," he said.

"Due 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."

If the judgement is upheld, it is expected to benefit Corbyn. The left-winger won almost 60% of the vote in 2015 and a poll from YouGov for The Times, of more than 1,000 Labour members between 15 and 18 July, put Corbyn on 56% and Smith on 34% based on first preference votes.