Keir Starmer has criticised Labour under Jeremy Corbyn for “turning on its staff” who blew the whistle about antisemitism, joining all the leadership contenders in saying the former officials should receive an apology and financial settlement.

Starmer said he had told Corbyn at the time it was wrong for the party to have put out a statement impugning the motives of former officials in the complaints unit who spoke to the BBC’s Panorama programme.

The ex-staff had told the BBC programme that the leader’s office interfered directly in the complaints process and their experience of the system had left them in despair.

In response, Labour criticised the programme as biased and released a statement saying: “It appears these disaffected former officials include those who have always opposed Jeremy Corbyn’s leadership, worked to actively undermine it and have both personal and political axes to grind. This throws into doubt their credibility as sources.”

Two of the former officials, Sam Matthews and Louise Withers-Green, later decided to take legal action against the party for libel.

Speaking at a hustings hosted by the Jewish Labour Movement, Starmer said: “I remember that programme well and being shocked by the response that was put out … I remember what I said to Jeremy. I said I’ve never been in an organisation that turns on its staff before, ever. Because what message do you think that sends not just to the ex-staff but current staff who speak out. They will be branded disloyal. I think it was utterly wrong that statement was put out and I said that directly the next morning.”

He said as a former director of public prosecutions he abided by the rule that “the leader of the organisation carries the can, stands up for what goes wrong and takes responsibility”.

Lisa Nandy, who got the biggest applause from the audience at the hustings for her answers, said: “We’ve got to do more than just settle … they are brave and they were accused of being disloyal. But what is more disloyal than not standing up for our Labour values? I would do more than just settle. I will make the Labour party a place that values and celebrates that sort of action.”

Rebecca Long-Bailey also said she would apologise to those staff members and settle the legal action. “I don’t think the party gave the right response to what came up on that programme. As the party of workers and trade unionists we should not under any circumstances have called out or attacked other members of staff. Whether we thought what they said was factually incorrect or not is a completely different matter. I think we should apologise about how we behaved and we should settle any claims that are made.”

Emily Thornberry said there had been a “culture of bullying” that had developed towards Labour staff, and criticised the redundancy notices issued to “footsoldiers” in contrast to senior staff who had kept their jobs.

Earlier in the hustings, the candidates were challenged about how they had spoken up against antisemitism. Starmer backed up Thornberry’s account that they both urged the leadership to do more to tackle antisemitism.

Starmer said: “We spoke up in shadow cabinet. We had a lot of rows. And I want to pay tribute to Emily. She spoke up loud and clear … Sometimes the row went on for the whole of the meeting.”

At Wednesday night’s BBC Newsnight’s hustings, Thornberry had said she could not recall Long-Bailey having done the same as a shadow cabinet minister, despite her claims to the contrary.

Nandy said she considered her position in Labour as a result of the resignations of Jewish MPs including Louise Ellman and Luciana Berger.

The hustings took place as the second stage of the contest draws to a close on Friday – the last day for constituency Labour parties and affiliates to nominate candidates. Starmer, Long-Bailey and Nandy are all through to the next round of membership voting but Thornberry is still a few endorsements short of the 33 parties needed to make the final ballot. All the deputy leadership contenders – Angela Rayner, Dawn Butler, Richard Burgon, Rosena Allin-Khan and Ian Murray – are through to the next round.

Long-Bailey will give a major speech in Salford, her constituency, on Friday in which she will seek to turn attention from Labour’s devastating election result to how the party wins next time.

In an appeal not to turn away from the radicalism of Corbyn’s policies, she will say she would not blame members for “looking for an easy option to win next time: give up on something here, be less forthright there and we can win, you might hope”. However, she will also warn that “the path of despair is also the path to defeat”.

She will say she was “worried after the election defeat that we might suffer a loss of confidence and step back from our principles and our ambitions” but go on to argue that the party must “forge a path to power” and claim that she is the only candidate who has that worked out plan to win the next election.

Rayner, the favourite to be deputy leader, also gave a speech on Thursday warning Labour not to abandon its commitment to lifelong learning, saying vocational education must be “the cornerstone of industrial policy”.

Speaking at the Unison Women’s Conference, the shadow education secretary will make the case for a system from early years to further and adult education that enables people to “take back control” and provide “practical answers” to the problems people face in the modern economy.