Now don't get me wrong, Mr Dalyell...

Are some of your best friends Jewish? Tam Dalyell's are. He told us so last week. Defending himself against the "preposterous" charge of anti-semitism, he also informed us that he and his children had worked on a kibbutz, that he had holidayed in Israel – but then so had Asif Mohammed Hanif of Hounslow, albeit with explosives in his belt – and that on occasions he writes affectionate obituaries of Jews, though whether the Jews are dead before he writes them he doesn't tell us.

Thus the Father of the House, knight of the mournful countenance, and champion of causes so lost they do not even know they are causes until he rides in to champion them – the man whom history not so much forgot as never noticed.

So why take umbrage? Why break a butterfly on a wheel? Well, a) because I feel like it, and b) because there is no folly so particular that it doesn't shed light on folly in general. Besides, by parading his prejudices as unwittingly as he has, by expressing such genuine surprise that anyone should find his words exceptionable, Tam Dalyell exposes the unexamined assumptions of his time and place.

What he has been saying, for those of you with your minds elsewhere, is that Jews punch politically above their weight, exercise an undue and disproportionate influence. As an off-the-cuff remark, dropped from the lips of a foolish fond old man, we would probably let it pass, but Mr Dalyell has been trying this on for size, to whoever will listen, for some time now.

Last year, for example, in an address to the Zayed Centre, an organisation "established in fulfilment of the vision of his highness Sheikh Zayed Bin Sultan Al Nahyan" – that vision having included one symposium denying the Holocaust and another validating the Protocols of the Elders of Zion – Dalyell told the assembled Arab delegates pretty much everything they wanted to hear about the criminality of Ariel Sharon, which is standard practice if you're going to accept that sort of an invitation, but didn't scruple either to let them into his pet theory on Jews and their over-influence. Whether or not the following were his exact words it is hard to tell, but he undoubtedly allowed the assembly to deduce from what he did say that "there were 400,000 Jews in Britain who enjoyed a very strong and stunning influence".

As I wasn't there in person, but have only the Zayed Centre's own report to go on, I am not sure whether that was "stunning" in the sense of Marilyn Monroe, or "stunning" as in what you do to a mullet. But I guess the latter.

Moving on from that, as in his recent interview with Vanity Fair, Tam Dalyell identifies a "cabal" of Jews, both in this country and in America, which is exercising undue influence over our Prime Minister. In the context of Jews and the power they are said to exert, we have, I think, wherever Mr Dalyell holidays, to take the word "cabal" as incendiary. It means to bring to mind a tradition of Jewish mysticism mistrusted by those who have always feared the hermetics of the Jews, at the same time evoking a suspiciousness of Jewish intrigue rooted in medieval ignorance and hatred. The Jew in cahoots with the devil to secure world domination blah blah. Now showing on Egyptian television. I don't much care whether any of this makes Tam Dalyell an anti-semite. There are already too many charges of racism flying about between the peoples of the world. Let's just agree the man has a problem with Jews.

Why else would advisers who happen to be Jewish (or look Jewish, or sound Jewish, or simply make Tam Dalyell "think" Jewish) become, in his imagination, a "cabal"? Why else would their influence, supposing it to exist, be a matter of such grave concern to him? And why else is he so watchful of the stain of Jewishness that he can detect its spread in ministers and advisers who, to the naked eye as it were, are barely Jewish at all? Peter Mandelson, for example, who lacks a Jewish mother and therefore cannot marry in an orthodox synagogue, supposing he should want to; Jack Straw whose single Jewish grandparent makes him but a quadroon.

Such genealogical curiosity has its antecedents in Nazi Germany, though I wouldn't dream of labelling Mr Dalyell, who holidays by the Dead Sea and writes obituaries of Jews, a Nazi. But the question has to be asked, why Jewish bloodlines compel his interest the way they do. And why he thinks that a distant Jewish relative leads ineluctably not only to undue influence, but undue influence in a sinister cause.

Enough Jews are prominent in their opposition to the policies of the present Israeli administration, let alone to the manner of their implementation, for Mr Dalyell to rest assured that wherever two or more of them are gathered there will not be an identity of pro-Israeli interest. They protest, they march, they offer themselves, some of them, as human shields against the Israeli army. But even were this not the case, even if it could be shown that every Jew in creation backed Israel to the hilt, where would be the wrong? Must a Jew empty his pockets of all traces of his Jewishness before the influence police deem him to be clean?

Interesting how seamlessly Dalyell moves between Israel and the Jews. It is not anti-semitic to be critical of Israel, we are forever being told. Nor is it. Nor should it be. But if the two are not identical, why is Tam Dalyell so quick to make them so? To what end of peace and understanding did he, in the same breath, and to an Arab audience, conflate the wrongs of Ariel Sharon and the 400,000 "stunningly influential" Jews of Britain?

Does he see Jew whenever he sees Israel? Does he see Israel whenever he sees Jew? More to the point, does he see criminality and then see Jew, or does he see a Jew and then see a criminality?