Credit to Chris Williamson for originality. Not many have suggested that Labour’s chief problem with antisemitism within its ranks is that it has been too apologetic to the Jewish community, that it has shown an excess of concern and contrition. Yet that is the argument the Derby North MP made to activists in Sheffield last week, in footage obtained by the Yorkshire Post.

“I’ve got to say I think our party’s response has been partly responsible,” he said. “Because, in my opinion, we’ve backed off far too much, we’ve given too much ground, we’ve been too apologetic.”

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This afternoon it was Williamson himself who was apologising for his “choice of words”, but his statement has not ended the matter. A Corbyn spokesman says that Williamson has now been issued with a notice of investigation into a “pattern of behaviour” but that he won’t be suspended while that inquiry is carried out. That’s unlikely to placate the party’s deputy leader Tom Watson, who wasted no time in branding Williamson’s apology “long-winded” and “not good enough”, adding that if it were up to him, he’d have removed the whip from Williamson already. Fellow MP Lucy Powell was no more charitable, telling Williamson that: “You have been touring the country whipping up conspiracy theories which are antisemitic and foster antisemitism.”

For, as it happens, the MP’s views on Jews were already attracting attention before the Sheffield footage emerged, thanks to his decision to host a House of Commons screening next Monday of a film made by Jackie Walker, currently suspended from Labour over allegations of antisemitism. Walker, you might recall, made the claim that many Jews were the “chief financiers” of the slave trade, a claim wholly debunked by specialist historians of the period but a staple feature of a particular strain of anti-Jewish rhetoric.

These interventions are hardly exceptional for Williamson. Indeed, it appears he has repeatedly leapt to the defence of people shunned either by Labour or the wider left for their overt anti-Jewish racism. In December the MP rushed to declare his support for Gilad Atzmon. The jazz musician has long been ostracised by pro-Palestinian activists for his record of anti-Jewish statements, ranging from his prediction that the day could come when some will be “bold enough to argue that Hitler might have been right after all” to his complaint that the US has undergone “Jewification”. Islington council had decided that it did not want Atzmon performing in one of its venues, and Williamson was quick to sign a petition demanding his reinstatement. When that triggered a chorus of protest, Williamson insisted he only knew Atzmon for his jazz work and was innocently unaware of his statements about Jews – a claim that falls apart under the lightest scrutiny. Why, exactly, did he think Islington had banned Atzmon – because they didn’t like his arrangement of the later works of Charlie Parker?

Play Video 0:41 Chris Williamson says Labour has been 'too apologetic' about antisemitism – video

Recall, too, Williamson’s stance on Peter Willsman, dropped last summer by Momentum from its slate of endorsed candidates for the national executive committee after Willsman had been recorded dismissing Jews’ fears about antisemitism as bogus and slamming Jews as “Trump fanatics”. That was too much for Momentum, but not for Williamson. He continued to back Willsman, and to do so loudly. Willsman was duly elected to the NEC.

Or perhaps we should recall the MP’s message to Jews in the immediate aftermath of the killing of 11 worshippers at prayer in Pittsburgh’s Tree of Life synagogue last October, the worst antisemitic attack in US history. Williamson decided that was the right time, several hours after news of the murders had broken, to tweet an attack on the British Jewish community’s representative body, the Board of Deputies. Some of his defenders tried to say he must have been unaware of the Pittsburgh massacre, but that defies credulity: surely if he was on Twitter, which he was, he would have seen news of the killings.

Why, then, given this track record – which led British Jews to conclude long ago that Williamson is a Jew-baiter, with a habit of defending Jew-haters – has Williamson not been disciplined? Jeremy Corbyn repeatedly tells us that Labour has zero tolerance of antisemitism, yet here it is showing a tolerance level way above zero.

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There are two possible explanations. The first is that the Labour leadership opposes Williamson’s stance but is fearful of acting against him, given the support he currently enjoys in the party, including on this subject. Witness the loud applause the MP got at that Sheffield meeting. The second explanation is that the leadership is not all that opposed to Williamson’s views, that indeed he functions as something of an outrider – staking out positions on, say, mandatory deselection of MPs, which the leadership is not wholly displeased to see aired.

In this context, it’s worth recalling Ken Livingstone’s testimony at his disciplinary hearing last year, making clear that when he toured media studios claiming, falsely, that Hitler supported Zionism, the Labour leader’s office raised not a word of protest – and that his media appearances were, in fact, tightly co-ordinated with the leader’s team. For a while, Livingstone was a licensed outrider for Jeremy Corbyn. Since Livingstone left the party, is it possible that Williamson has taken on at least some of that role?

Whatever the explanation, Labour’s insistence that the party is an implacable foe of anti-Jewish racism is rendered laughable every day that Chris Williamson remains a Labour MP. The anti-racist charity Hope Not Hate is right to demand he be stripped of the Labour whip. If the Labour party fails to make that move, then it will have passed judgment on itself – and that judgment will be damning.

• Jonathan Freedland is a Guardian columnist