Jeremy Corbyn is a self- professed anti-racist who never ceases to tell us of his opposition to all forms of racism, including antisemitism. He has yet to tell us exactly how he defines antisemitism. But one thing is clear: his definition is not the International Holocaust Alliance (IHRA) definition of antisemitism.
He has made it clear that any Labour member promoting "Holocaust denial, crude stereotypes of Jewish bankers, conspiracy theories blaming 9/11 on Israel, and even the one member who appeared to believe that Hitler had been misunderstood" has no place in the party.
But he and his supporters refuse to adopt the IHRA definition on ideological grounds -because they cannot accept the illustrative examples in the definition that show when criticism of Israel crosses the line into antisemitism.
What definition of antisemitism is the Labour Party disciplinary committee using?
Although Mr Corbyn is said to be concerned about the use of the explanatory examples in the IHRA definition, the reality is that he has no intention of accepting the IHRA definition. His ideology will not allow him to do so - and he wants to protect his friends (and himself) from being labelled as an antisemites.
When I first heard that Mr Corbyn had refused to accept the IHRA definition at his meeting with the Jewish leadership Council (JLC) and the Board of Deputies (BOD), it made me recall my own similar experience. Seven years ago this very week, my trade union, the University and Lecturers Union (UCU), at its annual Congress in Harrogate disassociated itself from the he EU Monitoring Centre on Racism and Xenophobia (EUMC) definition of antisemitism (from which the IHRA definition was derived).
The BOD and JLC were involved at the time as they tried - unsuccessfully - to persuade the UCU not to disassociate from the definition.
Whenever I spoke in anti-Israel boycott debates at UCU Congresses I was always listened to in silence. I never really understood before why this was so. But now I realise it was a form of 'blanking'. They were not interested in the views of the pro-Israel Jew and wanted instead to return to their anti-Israel fest as quickly as possible.
It wasn't personal but an ideological hatred of what I stood for. The election of Jeremy Corbyn as Labour leader in September 2015 provided his acolytes with the perfect opportunity to step up their demonisation of Israel and, worse, to cross the line into antisemitism by attempting to mask it as anti-Zionism.
This is exactly what happened when the far left took control of the UCU in 2006. Back then, we saw it as it as a takeover by a group who were on the periphery of Labour politics, and whose anti-Zionist policies made the union an intimidating, hostile and offensive environment for Jews.
It was, in hindsight, the model for what has since happened in the Labour Party - with fringe racist anti-Israel policies crossing over into mainstream politics, and with a resulting rise in claims of antisemitism within the party.
Between 2007 and 2011, the UCU Congress was gradually cleansed of any delegates willing to speak up on behalf of Israel and pro-Zionist Jews. By 2011 I was the sole remaining Zionist at Congress.
A similar process is now taking place in the Labour Party. MPs who speak out against antisemitism in the party are accused of disloyalty to Corbyn or part of a plot to remove him as leader.
There are signs that the Corbynistas want to do what they did in the UCU - to cleanse the Labour Party of Zionists.
Now is the time for our communal leaders to put in place a strategy for when Jeremy Corbyn eventually formally refuses to accept the IHRA definition, as he surely will.
It won't be easy. In 2002 the BOD met with the academic unions, who had backed the call for an academic boycott of Israel, and warned them that "those who engage in anti-Israel rhetoric should have regard to the antisemitic consequences."
If the unions and their far left supporters refused to take on board concerns first raised sixteen years ago, then we need more than the vague promises to deal promptly with a backlog of alleged antisemitism disciplinary cases.
This may convince the general public that the Labour Party is tackling antisemitism but history shows it's not real.
Ronnie Fraser is Director of the Academic Friends of Israel. He has written about his legal action against the UCU in the forthcoming book, Anti-Zionism on Campus to be published in May by the Indiana University Press