Mi Yehudi? Who is a Jew? This question is as old as Judaism itself. The normative definition — espoused by orthodox rabbinical authorities — is that a Jew is someone born of a Jewish mother or converted to Judaism by a reputable ecclesiastical court.

But of course this answer merely begs other questions. Matrilineal descent was not uniformly emphasised even in biblical times (see, for example, Deuteronomy, x, 15) and it is now widely accepted that emphasis on the mother rather than the father was primarily an expedient: in the days before DNA testing one could never be sure of the father’s identity but always of the mother’s. In any case, today there are well-established varieties of non-Orthodox Judaisms that recognise as Jewish anyone who has a Jewish parent of either sex.

As for conversion, what is meant exactly by the phrase “reputable ecclesiastical court”? Who decides the question of repute? There are in the UK today women who have undergone conversion through the auspices and with the imprimatur of the Chief Rabbinate of the State of Israel — the Jewish state — but whom the Chief Rabbi of the London-based United Synagogue refuses to recognise as at all “Jewish”. These mothers and their children are Jewish in Israel, but somehow, en route from Tel Aviv to Heathrow, they apparently cease to be so. I recognise them and their offspring as 100 per cent Jewish; the Chief Rabbi Sir Jonathan Sacks does not.

In bygone eras this would have mattered only in the Jewish world, and would have been of merely curiosity interest to the non-Jewish. The current battle of wills over who controls admission into Jewish schools in England means that this is no longer the case. The recent decision of the Court of Appeal has brought this issue to a head.

Two years ago the child “M” was denied a place at the prestigious Jews’ Free School (JFS), northwest London, because and only because the child’s mother had been converted to Progressive Judaism by a Progressive ecclesiastical court, which the Office of the Chief Rabbi does not regard as reputable. The Appeal Court has now ruled that “M” was the victim of racial discrimination. “Jews”, the Appeal Court has determined (or rather, confirmed) “constitute a racial group defined principally by ethnic origin and additionally by conversion, and . . . to discriminate against a person on the ground that he or someone else either is or is not Jewish is therefore to discriminate against him on racial grounds.”

When the Race Relations Act was passed in 1976, many British Jews were vocally unhappy that they might be legally categorised in racial terms in order to take advantage of the protection afforded by that legislation.

That Jews are so protected is due to the impact of subsequent judge-made law, notably the Mandla case of 1983, which actually concerned the Sikh community. In ruling that Sikhs were not a religious group (and thus outside the protection of the Act), but rather a racial or ethnic group (and thus within its protection) the law lords set forth a definition of ethnicity that clearly applied and applies equally to Jews.

To quote Lord Fraser of Tullybelton: “A group defined by reference to enough of these characteristics would be capable of including converts, for example, persons who marry into the group, and of excluding apostates. Provided a person who joins the group feels himself or herself to be a member of it, and is accepted by other members, then he is, for the purposes of the Act, a member.”

We Jews cannot have it both ways. We cannot shelter under the safety of the 1976 Act when it suits us — for instance in relation to employment law — but then, when it does not suit us (or some of us) deny that we constitute an ethnic group and affirm that we are merely and exclusively a set of religious communities.

The entire claim to Jewish national self-determination is in fact based upon the argument that the quality of being Jewish is much more than — and is, in fact, something other than — observing a collection of religious precepts. There are many Jews, in Israel and in the UK, who observe none of the precepts of any of the branches of Judaism — Orthodox, Reform or Ultra-Orthodox. They are Jewish nonetheless.

Some Anglo-Jewish spokesmen have declared that the Appeal Court’s recent ruling constitutes an assault upon religious freedoms, and that the Lord and Lady Justices of the Court have arrogated to themselves the right to decide who is a Jew.

They have done nothing of the sort. The judgment itself explains that although the refusal of the JFS to admit “M” was tantamount to racial discrimination, “this does not mean . . . that no Jewish faith school can ever give preference to Jewish children.

“It means that, as one would expect, eligibility must depend on faith, however defined, and not on ethnicity.”

Jewish ecclesiastical authorities in the UK are as free now as they have ever been to decide whom to recognise as Jewish. But the governors of Jewish schools must now abide by a different set of rules, grounded primarily in religious practice. It is common knowledge that the JFS currently admits Jewish pupils from irreligious backgrounds. In future its admissions policy will have to reflect this fact, and be fair, therefore, to all such parents who desire a JFS-type Jewish education for their children.

Geoffrey Alderman is Michael Gross Professor of Politics & Contemporary History at the University of Buckingham and the author of Modern British Jewry