IT creates an obvious presentational problem when, on the eve of the day you planned to campaign on race and faith, the leader of a major faith community issues an unequivocal condemnation of your party.

The ideal response, however, is not continuing to insist that Labour doesn’t have a problem with anti-Semitism, while a vocal minority of supporters maintain that a) the Chief Rabbi is a Conservative stooge, b) Israel is a racist state, and c) the whole thing is a plot by Mossad or the banking system because Jews (who are all rich, sinister, powerful, manipulative and Tories) hate Jeremy Corbyn.

If you don’t believe that anyone could, with a straight face, present such obviously racist claims as evidence that the Labour Party is free of “anti-Semitism and all forms of racism” (as the anti-Semites always put it), two minutes on any form of social media will comprehensively disabuse you of the notion.

Momentum activists who think it axiomatic that you should uncritically back any self-designated victim (in, for example, the Me Too, Black Lives Matter, or LGBT+ movements) readily dismiss the fears of what polling suggests are 85 per cent of British Jews as a “smear” weaponised against a saintly leadership free of any taint of racism. Jeremy Corbyn, some of them will assure you, fought at Cable Street against Oswald Mosely’s fascists.

This fantasy (the Battle of Cable Street was 13 years before Corbyn was born) is only the most ludicrous example of the detachment from reality that some Labour extremists have adopted on this issue.

Three years ago the party attempted to dismiss the idea that there was any problem with an inquiry conducted by Shami Chakrabarti (who indicated her independence by immediately joining the party, concluding within weeks that anti-Semitism was not widespread, and then going straight into the Lords as a Labour peer).

Unsurprisingly, the problem did not go away after this transparent whitewash. A steady stream of Labour MPs and former supporters criticised or left the party (frequently after appalling and blatantly racist abuse and threats from other members). And while some senior figures – notably Ken Livingstone and Chris Williamson – were expelled from the party, many remain.

There are, unfortunately, racists in every political party, and it’s reasonable to expect their leaderships to act quickly to investigate, and where necessary, expel those responsible. But instances of Tory Islamophobia or cybernat racism are fewer, more readily disowned, and largely taken seriously, even if not always tackled as thoroughly as they should be.

Labour’s problem, though it is with a minority of the membership, is endemic. Worse, the leadership is in total denial, even though 70 per cent of party supporters think it’s a significant problem. It is different from the accusations of racism or anti-Semitism within other parties, because of the inadequacy of the response so far, and the ambivalence of Mr Corbyn, who has in the past shared a platform with people who have expressed violently anti-Jewish sentiments.

There are a couple of reasons why a coterie in Labour’s leadership and amongst its more militant supporters simply refuse to acknowledge this, and they are tied in with Mr Corbyn’s other attitudes.

While protesting his hatred of racism, he has always viewed the Israeli state as the villain, and sympathised with its opponents, even when they had clear terrorist connections or virulently anti-Semitic views. This is of a piece with his inclination to side with terrorists and dictatorial regimes rather than Western democracies.

Despite his claims, he has never been involved in “peace processes”; he may say he deplores violence “on both sides”, but in practice he supported the aims of the IRA, the PLO, Hamas or Hezbollah.

These “anti-Imperialist” attitudes have been the norm on the hard Left for decades, and Mr Corbyn and his acolytes show no sign of recognising their tendency to slip into outright anti-Semitism – as was shown by the party’s extreme reluctance to adopt the International Holocaust Remembrance Alliance’s definition of anti-Semitism.

The other obviously problematic area – shown by Mr Corbyn’s initial defence of an outrageously anti-Semitic mural, on the grounds that it was not racist but a condemnation of capitalism (for which he did later issue a sort of apology) – is the apparently unconscious way in which so many on the hard Left often use Zionism, or in some circumstances “international banking” or just “capitalism”, as if they were synonyms for some global Jewish conspiracy.

This is an obviously racist tic when it’s seen on the White Supremacist far-Right, but too many on the Corbynista Left seem unable to grasp that their wild allegations about “the Rothschilds” or the “Israeli state’s fascism” amount to the same thing.

What Labour is missing most of all is that Jewish concerns are coming especially vocally from former supporters, and even MPs and peers, who would like to vote Labour, but conclude that it is morally impossible while Mr Corbyn remains leader. That’s not “Tory smears”; it’s genuine worry and dismay from party loyalists who’ve been not only abused but betrayed.