On Tuesday, Labour’s national executive committee must take a fateful decision: whether to adopt in full the International Holocaust Remembrance Alliance’s definition of antisemitism or to persist with a definition amended by the Labour party, in a move condemned as “insulting and arrogant” by a cross-section of Jewish leaders. It comes at the end of a summer that has seen the party become engulfed in internal battles about antisemitism, entirely neglecting its job in holding the government to account.

Labour’s disciplinary processes for members charged with antisemitism have long been under scrutiny. They were strongly criticised by the 2016 home affairs select committee inquiry into antisemitism. Even as growing numbers of cases within Labour’s ranks have come to light, the party has failed get to grips with the problems in its processes. On the contrary; it has preposterously chosen to pick a fight about the legitimacy of an internationally recognised definition of antisemitism that has been adopted by 130 councils, the police, the judiciary and the Crown Prosecution Service, as well as 30 other countries.

Labour’s argument is that the IHRA definition risks precluding legitimate criticism of the Israeli government. That does not hold water. The IHRA says that manifestations of antisemitism “might include the targeting of the state of Israel, conceived as a Jewish collectivity. However, criticism of Israel similar to that levelled against any other country cannot be regarded as antisemitic.”

This paper has always argued there is plenty on which to unreservedly condemn successive rightwing Israeli governments, from the killing of defenceless Gazans, to the aggressive expansion of illegal settlements in Palestinian territory, to the shamefully discriminatory treatment of its Arab citizens. None of that falls foul of the IHRA definition.

Labour’s alternative definition says criticism of Israel will not be treated as antisemitic unless “accompanied by specific antisemitic content (such as the use of antisemitic tropes) or by other evidence of antisemitic intent”. This is in breach of the Macpherson principle, drawn up in the wake of the murder of Stephen Lawrence – that a racist incident is one perceived to be racist by the victim. Intent should never be the litmus test.

More than 60 British rabbis, from Judaism’s most progressive to its most orthodox traditions, wrote an unprecedented letter to the Guardian in July asking Jeremy Corbyn to adopt the full IHRA definition. That plea has gone ignored. It is not the Labour party’s right to choose how antisemitism gets defined. This is especially true given the party has so comprehensively lost the trust of Britain’s Jewish community.

In recent weeks, things have got worse. The party targeted Margaret Hodge, a Jewish MP, for disciplinary action for accusing Corbyn of antisemitism. And it has emerged that Corbyn himself made a statement in 2013 that many regard as antisemitic.

That statement – that a group of “silent Zionists” at an event being addressed by the Palestinian ambassador in Britain “don’t understand English irony”, despite “having lived in this country for a very long time” – smacks of casual, unthinking racism. It suggests that Labour’s leader does not understand the boundary between legitimate criticism of Israel and its supporters and antisemitism.

Of course antisemitism is not limited to the left. But the way antisemitism so often manifests itself – painting Jewish people as a powerful, malign, controlling influence on the world rather than as inferior objects of derision – means some on the left have been particularly susceptible to it, even as they proclaim themselves to be antiracist. Corbyn has utterly failed to grapple with this. Labour will never remove the poison of antisemitism until it acknowledges that some parts of the left have been breeding grounds for antisemitism, even as they call out other forms of racism.

The only way for Corbyn to begin to redeem himself would be to learn from the Labour MP Naz Shah, who issued a heartfelt apology after sharing an antisemitic social media post and has since been widely praised by the Jewish community for her efforts to reach out and understand why what she did was wrong. And the party itself must adopt the full IHRA definition of antisemitism at the meeting of its national executive on Tuesday. Nothing less will do.