Anti-Semitism is racism plain and simple. There would be outrage, and quite rightly so, if anyone said a British born Muslim could not be trusted to serve loyally as an ambassador to a Muslim country. We did not question Francis Campbell, the first Catholic to be appointed ambassador to the Holy See. So why is it acceptable to question the loyalty of the Jew but not the Muslim or the Catholic? Where are our antennae about this kind of anti-Semitism? Where is our moral clarity?

Paul Flynn is not an anti-Semite. But his recent remarks, about the British Ambassador to Israel, Matthew Gould, gave expression, surely inadvertently, to a very old anti-Semitic idea: the eternally 'divided loyalty of the Jew.'

At the Public Administration Select Committee on 30 November, Flynn complained that "the ambassador has proclaimed himself to be a Zionist" and then raised doubts about Mr Gould's loyalty. Flynn then compounded the problem by telling the Jewish Chronicle that Britain needed "someone with roots in the UK [who] can't be accused of having Jewish loyalty."

Today, Flynn has apologised and withdrawn his remarks, following a meeting held last Friday with the Chief Whip. "I greatly regret the interpretation that has been placed on them and I fully understand why offence was given...There is no reason that anyone of any race or religion should be debarred from public office."

Good. In the past Jews were depicted a 'rootless cosmopolitans' loyal to the wandering tribe and not the nation in which they would never be more than an interloper. In the present Jews are depicted as the 'Zionist' or part of the 'Israel lobby,' loyal to Israel not the nation in which he or she is, once again, no more than an interloper.

This is not a left-right issue. The Conservative MP Robert Halfon said "Mr Flynn's actions betray an extraordinary mindset on the left, that allows normally highly intelligent and engaging individuals to lose all sense of proportion when the word 'Israel' is mentioned" said the. The hard-left pro-Palestinian campaigner Owen Jones was equally outraged at the encouragement for anti-Semitism Flynn's tirade had encouraged.

Jenni Frazer noted at the Jewish Chronicle that 'Flynn has now brought this attitude into respectable conversation.' In truth the attitude has been there for a while. Back in 2002 the New Statesman cover featured a gold Star of David impaling the Union Jack and the words 'A kosher conspiracy?...Britain's pro-Israel lobby.' As the online journal Engage has pointed out the message was 'What about these Jews, whose classic apart-ness, epitomized by their dietary habits (keeping kosher), pits their own self-interest over that of the supine UK (graphically portrayed as if it were a recumbent trophy base)?'

Usually, when this kind of anti-Semitism raises its head the left sobers up and apologises. Back in 2002 the editor of the NS Peter Wilby admitted he had 'gotten it wrong' because '(t)he cover ... used images and words in such a way as to create unwittingly the impression that the New Statesman was following an anti-Semitic tradition that sees Jews as a conspiracy piercing the heart of the nation.'

But the dual loyalty slur is still with us, as Flynn's comments showed. In fact with the publication in 2007 of John J. Mearsheimer and Stephen M Walt's flawed but deeply influential book The Israel Lobby it has taken on a new respectability.

And that is why the absence of an on-the-record condemnation of Flynn's remarks by Labour Party leader Ed Miliband has drawn a rebuke from Jenni Frazer blogging at the Jewish Chronicle: "I have rarely felt such a sense of disappointment in a Labour leader as I do today in Ed Miliband."

In fact the Labour leader spoke powerfully to the recent Labour Friends of Israel dinner about his commitment to the state of Israel;

I wouldn't be here today if it wasn't for the State of Israel and what it has achieved, and I wanted to make that clear. I'm grateful to Israel, I respect Israel, I admire Israel and that is why I'm proud to be here to be here, to be part of Labour Friends of Israel. And I give you my word that under my leadership I will ensure that the Labour Party remains a strong and steadfast friend of Israel.

Because he went on to express his absolute commitment to the two state solution and his vision of 'Israel and Palestine living side by side; and with each enjoying self-determination and mutual recognition" this eloquent and intelligent Labour Leader now can restore moral clarity to the debate by not just condemning, but by using his bully-pulpit to educate. This is what President Obama called a 'teachable moment.' Ed should seize it.