A senior member of Jeremy Corbyn‘s shadow cabinet has admitted the party has an “ongoing problem” with antisemitism and the processes it uses to deal with it.

The shadow foreign secretary, Emily Thornberry, said that Labour should not be “going for” former officials who blew the whistle on how it handled antisemitism in the party, and called on Mr Corbyn to invite the Equality and Human Rights Commission in to help the party improve its systems for handling allegations.

But she criticised deputy leader Tom Watson for pointing the finger of blame at general secretary, Jennie Formby, at a time when she is undergoing chemotherapy treatment for cancer, saying: “I think that is a mistake. We know that she’s ill. I think it’s completely inappropriate to personalise this.”

The Islington South MP’s comments came as two whistleblowers featured in a BBC Panorama broadcast on Labour antisemitism said they plan to sue the party over its response to their claims.

Former officials Sam Matthews and Louise Withers Green said they believed they had been defamed by Labour in its response to their allegations.

The programme, shown on Wednesday, included claims that senior figures including Seumas Milne, Jeremy Corbyn’s communications chief, and Jennie Formby had interfered in antisemitism investigations.

In its response, Labour said the allegations came from “disaffected former officials” opposed to Mr Corbyn’s leadership who had “personal and political axes to grind” casting doubt on their “credibility” as sources.

Mark Lewis, the prominent media lawyer who is acting for the pair, told The Observer: “These are very serious libels. Those representing the Labour party have acted in a way that set out to destroy the reputations of the whistleblowers.

”In their effort to destroy these people, they have left it for the courts to decide who is telling the truth. It is ironic that the bosses at the workers’ party have decided to go against the workers.“

Jeremy Corbyn delivers his speech during the 135th Durham Miners Gala (Getty)

Labour denied the comments were defamatory and said it would contest any legal action.

“These are justified statements of opinion. Any claims will be vigorously defended,” a spokesman said.

Speaking at the the Durham Miners’ Gala on Saturday, Mr Corbyn himself said programme contained “many, many, inaccuracies” and had adopted a “predetermined position”.

But veteran MP Dame Margaret Hodge said it was “utterly deplorable and a complete abuse of power” for the party to use lawyers to try to silence former workers from speaking out about their experiences.

And Ms Thornberry told BBC1’s Andrew Marr Show: “I think that we shouldn’t be going for the messengers, we should be looking at the message. I think that is what is important.

“Nobody can pretend that there isn’t an ongoing problem within the Labour Party about antisemitism, about our processes for dealing with it.”

She acknowledged that the party had concerns about the way the documentary was produced.

But she said: “It’s fair to say that Panorama didn’t really look at the way we had improved our processes, but I don’t pretend that they are perfect because they are not...

“This has been going on a very long time and despite the efforts of our general secretary and the fact that she has improved processes and done a lot of work on it, it still has not been sorted out.”

Dame Margaret, who is herself Jewish, told Sky News’s Ridge on Sunday: “These are young committed idealistic Labour Party activists and Labour Party workers and they have been crushed by what has happened to them.

“It was utterly deplorable and a complete abuse of power that the leadership’s reaction was simply to try to pursue these people with lawyers and try to shut them up.

“Anybody who watched that programme would have seen that they are committed, honest people with integrity who care about the Labour Party. Three of them had been driven into mental health conditions – one had a breakdown, one had suffered depression and one had contemplated suicide.

Under pressure: Jennie Formby, Labour general secretary (AFP/Getty)

“For the leadership of the Labour Party to dismiss that as ‘disaffected workers’ I think is intolerable and unacceptable. It’s a real abuse of power and I think the Labour Party should really reflect and think again.”

The Barking MP was subjected to party disciplinary action last year after telling Mr Corbyn he was an antisemite.

“To be honest I’ve seen nothing in the past year that has caused me to change my mind, both in the incidents of antisemitism that have emerged and in the further details we’ve had of Jeremy Corbyn himself – the sort of people he’s met, the fact that he went to a wreath-laying for terrorist people,” she said.

She called on Labour to set up an independent body to investigate disciplinary cases, saying the internal system had been “corrupted by political influence from the leader’s office”. She said there should be immediate expulsions for those accused of antisemitism and called on the party to publish its submission to a Equality and Human Rights Commission inquiry into Labour and to cease all actions against whistleblowers.

Labour MP Margaret Hodge responds to Panorama episode on alleged antisemitism in party

Dame Margaret said she would not leave a party she has been a member of for more than half a century, but warned that others would.

“I don’t know how many incidents of antisemitism we have to have on our television screens or in our newspapers for the party leadership to stand up and really listen,” she said. “There seems to be a dogged determination not to listen.I think we are at a tipping point. If the leadership don’t start to listen now there will be many more people who will feel so uncomfortable in the Labour Party that they just can’t stay in.””

She offered her support to Mr Watson, after the Unite general secretary, Len McCluskey, launched a blistering attack on the deputy leader, telling crowds in Durham: ”I have a simple message for Tom Watson and his pals in the media – a simple message to Tom and his pals: You should f**king well be ashamed of yourselves.”

Dame Margaret said: “I applaud Tom Watson. He has been calling this out for a long time. He and I, I think, share the view that we are fighting for the soul of the Labour Party.”

The shadow chancellor, John McDonnell, insisted Labour was “getting on top” of the problem.

“There are always lessons to be learnt, but I think the way in which Jennie Formby has operated, implementing the measures, is getting on top of this,” he told BBC Radio 4’s World This Weekend.

“We have now got the EHRC inquiry. We want to learn lessons from that as well and we want to be the party that demonstrates we are an anti-racist party and can perform an anti-racist role in society as a whole.”

Mr Matthews and Ms Withers Green – who broke non-disclosure agreements to speak out – were among eight former party employees featured on Panorama.

Mr Matthews told The Observer: “The Labour party is choosing to ignore the central charges of antisemitism raised by myself and other whistleblowers on Panorama, and instead, they have engaged in a concerted campaign to damage my name.”

Ms Withers Green told the paper she was “incredibly disappointed” that the party had not taken action on the issues raised in the programme.