Three Labour peers have quit the party over its handling of anti-Semitism.

Lord Triesman, Lord Darzi and Lord Turnberg announced their decision inside an hour of each other on Tuesday afternoon.

The triple resignations came 24 hours before a BBC Panorama investigation into the party’s anti-Semitism problems was due to be screened last night.

In a scathing attack on the party leadership, Lord Triesman, in his resignation letter to Labour’s leader in the House of Lords, Baroness Smith, said he was resigning the whip with immediate effect.

“It is a painful decision arrived at with great sadness,” he noted, adding that the decision had become “inevitable”.

In a stinging attack on the party, Lord Triesman said that day by day the extent and depth of anti-Semitism had become clearer in the top leadership and National Executive Committee.

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

Triesman said the Party had slipped into the “familiar gutter of so many of the hard left” and “old tropes about the secret wiring connecting Jewish entrepreneurs and use of wealth to exercise secretive control can be heard almost daily”.

He added that the party was “very plainly institutionally anti-Semitic, its leader and his circle are anti-Semitic, having never once made the right judgement call about an issue, reflecting deep prejudice. The number of examples is shocking.”

He also noted it was not a “safe political environment for Jewish people or other opponents of anti-Semitism” and it was time to recognise the reality.

Lord Triesman concluded, “I always said it was worth hanging on to fight so long as there was a prospect of winning. I now don’t believe with this leadership there is.”

Lord Darzi, an Armenian survivor of the Armenian genocide, will now sit as an independent peer as he has “zero tolerance to anti-Semitism, Islamophobia or any other discrimination against religion or race”.

The former Health Minister added that the decision had not been taken lightly.

Lord Turnberg told BBC Newsnight his differences were with the party leadership and machine not supportive Lords colleagues who shared his values.

He added that it was not just about policies on foreign affairs but overt anti-Semitism that permeates the party machine that is no longer possible for me to tolerate.”

A Labour party spokesperson accused the three Lords of making “false and offensive claims”.

“The Labour party at all levels is implacably opposed to anti-Semitism and is determined to root out this social cancer from our movement and society,” the spokesperson said.

“Labour is taking decisive action against anti-Semitism, doubling the number of staff dedicated to dealing with complaints and cases. And since Jennie Formby became general secretary, the rate at which anti-Semitism cases have been dealt with has increased four-fold.

“Our records show that anti-Semitism cases that have gone through the stages of our disciplinary procedures since September 2015 account for about 0.06% of the party’s membership.

“This represents a tiny minority, but one anti-Semite is one too many, and we will continue to act against this repugnant form of racism.”

The triple resignation follows the furore over Labour MP Chris Williamson who faces a new investigation into alleged anti-Semitism by a specialist panel.

Members of Labour’s governing body’s disputes committee referred his case to the panel following a meeting. A date has to be set.

Williamson was controversially readmitted to the party following an investigation into anti-Semitism allegations.

The Derby North MP was suspended last February over a “pattern of behaviour” going back months but his punishment was lifted by a three-person NEC panel despite a recommendation from party staff he be referred to the next stage of Labour’s disciplinary process.

Williamson received a formal warning after being found to have breached party’s rules.

By Adam Moses