An email from the Labour leader’s camp raised what it called “legitimate” questions about the allegiances of those taking part in the hustings due to be broadcast on Wednesday.
The memo, sent to SkyNews and Labour HQ, raises what it calls a potential “conflict of interest” in pollsters Survation being used to build the audience for the programme.
The Corbyn camp suspects that Survation is doing polling work for the Smith 2016 campaign and is demanding assurances that there will be scrupulous balance in the audience Sky debate.
Both SkyNews and Survation have offered such assurances, HuffPost UK has been told, but the Corbyn camp are demanding more clarity as the TV debate is the last in the Labour leadership race.
“It’s 50-50 at the moment as to whether we will take part,” one Corbyn source said, adding that it would be a “dealbreaker” if they continued to feel the audience was unrepresentative.
“We are still making the decision. There is still cause for concern and we don’t want to find out after the programme that we were proved right.”
A final decision could be taken as late as Wednesday morning on whether Corbyn takes part.
The row came as Smith told the BBC suggested that he could stand again to challenge Corbyn, even if he loses this year.
‘Corbyn v Smith – The Battle For Labour’ is set to be the last TV hustings between the leadership pair, just one week before the ballot closes.
An email to SkyNews from Sam Tarry, Corbyn’s director of communications, strategy and campaigns, set out the concerns about the programme.
It states that “we have some concerns” over the role of Survation, which it suggests has links to Smith’s private polling and phone banking operation.
“I think it is legitimate to be concerned and to raise questions,” Tarry said. “Can we be reassured that there will be balance..?”
The email was then forwarded to party general secretary Iain McNicol.
McNicol replied: “I know that you had expressed some concerns previously but believed these to have been resolved and the event subsequently confirmed.
“As you will know, we have now emailed London members inviting them to attend and advertised the event on our website. I hope that we are able to proceed as planned as this is one of the only two remaining debates before the close of ballot.”
The final debate will be a Jewish News hustings on Sunday.
The Corbyn campaign has already pulled out of previous hustings, due to be organised by Channel 4 News, the Daily Mirror and the Guardian, claiming worries about bias.
HuffPost UK has been told that Survation has given a written assurance that its audience selection process will be scrupulously fair and professional.
SkyNews has used the polling firm successfully for previous live televised events, including EU referendum debates featuring Corbyn, David Cameron and Michael Gove.
Pollsters usually protect their client confidentiality on private polling, although any financial links have to be declared in the usual Electoral Commission and MPs’ register of interests in the usual way once a contest is over.
The Smith campaign came under fire on Twitter recently when a photo emerged of their candidate standing next to a whiteboard with a phonebank login which had ‘Survation’ as its password.
Corbyn ally Emily Thornberry accused Sky News’ Dermot Murnaghan at the weekend of ‘sexism’ after he asked what she called “pub quiz” questions about foreign leaders.
The Smith campaign has ridiculed Corbyn supporters for ‘conspiracy theories’ over alleged media bias during the campaign, citing unfounded fears about the BBC Question Time’s host David Dimbleby even before he chaired one hustings.
Smith told the BBC on Tuesday that Corbyn was “delusional” if he thought he would beat the Tories.
Asked whether he would stand for the leadership again if Corbyn wins, he said: “I am not ruling anything in or anything out,” adding that this was “a hypothetical question for the dim and distant future”.
UPDATE: On Wednesday morning, the Corbyn campaign said they had received sufficient reassurances about audience balance and would go ahead with the debate.