Three Labour peers have quit in protest at Jeremy Corbyn’s failure to tackle anti-Semitism and his wider policies on Brexit and defence.

Former ministers Lord Triesman and Lord Darzi, along with Lord Turnberg, resigned the parliamentary whip with scathing assessments of Corbyn’s leadership.

On the eve of the BBC Panorama investigation into anti-Jewish abuse within Labour, the trio claimed that both the leader and his close team were responsible for making the party “institutionally anti-Semitic”.

Lord Triesman, a former foreign minister and Labour general secretary under Tony Blair, declared that the extent of anti-Semitism among the “top leadership” had became clearer day by day.

Lord Turnberg, who like Triesman is Jewish, attacked “the overt anti-Semitism that permeates the party machine”.

All three revealed their resignations to BBC’s Newsnight on Tuesday, amid speculation that former party staff use whistleblowing rights to lay bare fresh details of Labour’s handling of cases of anti-Jewish discrimination.

The Equalities and Human Rights Commission is currently conducting a statutory investigation into Labour’s anti-Semitism, the first time a political party has been subjected to such a probe since it ordered the BNP to stop discriminating against black people.

A further clutch of peers could also quit the party whip, insiders claimed.

In his letter of resignation to Labour’s Lords leader Baroness Smith, Triesman said the party had “slipped into the familiar gutter of so many on the hard Left” of blaming the excesses of capitalism on a Jewish conspiracy.

“Anti-Semites are shielded and solid serious party members are thrown out unceremoniously,” he wrote.

“And each new manifestation is followed by a grim parade of social media messages directed at Jewish party members. The experience of life in the party has become sickening.

“My sad conclusion is that the Labour Party is very plainly institutionally anti-Semitic, and its leader and his circle are anti-Semitic having never once made the right judgment call about an issue reflecting deep prejudice.”

Triesman added it was “impossible to take seriously” Labour’s “vacillation” on Brexit policy, and Corbyn’s support for Russia’s Vladimir Putin.

Asked by Newsnight what evidence he had that Corbyn was himself anti-Semitic, Triesman said he had “not once, never” made the right judgement call on the issue.

“And in those circumstances, it’s hard not to come to the conclusion that he either is indifferent to the problem or he is part of the problem.”

Lord Darzi, whose family was caught up in the 1915 Armenian genocide, said that he would now be sitting in the Lords as an independent.

“I have zero tolerance to anti-Semitism, Islamophobia or any other discrimination against religion or race. This decision has not been lightly taken,” he told Newsnight.

Lord Turnberg added: “I am very saddened to have had to resign the Labour whip not least because my differences lie with the party leadership and machine and not with my very supportive colleagues in the Lords who share my values.

“It is not just the policies on foreign affairs – pro-Russia, pro-Venezuela anti-America – and not just Brexit vacillation and by-passing parliamentary opinion, but the overt anti-Semitism that permeates the party machine that is no longer possible for me to tolerate.”

Baroness Smith told the Parliamentary Labour Party (PLP) last week of her own deep concerns about the saga, declaring the EHRC investigation “brings shame to our party”.

“We have failed to give any confidence, not just to the Jewish community, but to the public, our voters and party members that we are determined to do everything we can to root out such a cancer from our party,” she said. 

“No ifs, no buts, no qualifications or hesitation. This strikes to the very core of our existence. 

“It hurts too many of our Jewish members who don’t see the Labour Party as a safe space. And it diminishes us all.

“I believe it can be fixed. We’re right to look at structures and procedures and to overhaul when needed. But political will and determination from everybody in a leadership position is absolutely essential. Or we fail.”

In an interview with the BBC, Corbyn said: “Anti-Semitism is an absolute evil in our society. It’s an evil in any country where it raises its head. 

“There is no place whatsoever for anti-Semitism in my party, in our community, in our society or in our world. We will do everything we can to drive out anti-Semitism.”

A spokesman added: “We completely reject these false and offensive claims [by the peers].” 

Labour sources said no evidence or examples had been provided to back up Triesman’s claim that “anti-Semites are shielded”. 

They added his letter made untrue claims which misrepresent the Labour Party’s position on a number of policy issues.

Suspended Labour MP Chris Williamson faces the fresh threat of expulsion from the party after the ruling National Executive Committee’s dispute committee decided to reopen a probe into his alleged anti-Semitism.