THE PERCENTAGE of British Jews who find spouses or life-partners outside the faith is rising a little over time, but the share remains much lower than it is among American Jews. Those are the main conclusions of a new survey of the Jewish community in Britain, whose size is ticking upwards after decades of decline owing to lowish birth rates, assimilation and emigration. In 1955, there were more than 400,000 Jews in the United Kingdom; the 2011 census put the figure at 270,000, a rise of 1.1% over 2001. The new study's author, David Graham, and other pundits reckon the census number, based on a voluntary question, is too low: 290,000 might be nearer the mark. Mr Graham found signs both of conservatism and of freer life-choices, but the former seem more striking. As you might expect, British Jews are undergoing some of the social changes observed in society as a whole. They are marrying later, increasingly likely to live together informally before marriage or indefinitely. But this is still a relatively traditionalist and compact segment of society. As of 2011, over 124,000 Jews, or six in 10 Jewish adults were living in couples: that is a higher proportion than for any other ethnic or religious group. Of these couples, 89% were married and the remainder cohabiting.

Among Jews who had married since 2010, about 26% had found non-Jewish spouses. That is less than half the equivalent number in the United States, a comparison that has remained roughly stable since the 1970s. As Mr Graham notes, among American Jews marriage outside the faith is widely accepted; indeed the argument is made that exogamy is a sign of a community's health and confidence, and that it ultimately enlarges the Jewish population, as long as more than half the children of inter-married couples are raised Jewish. But Mr Graham finds plenty of evidence of the opposite phenomenon in Britain; "in-marriage" helps to keep community intact and loyal to its heritage. By a whole range of indicators, from observing the Sabbath to keeping kosher rules, "in-married" couples were found to be much closer to the Jewish tradition than mixed ones. Almost all (96%) of children with two Jewish parents were raised as Jews. But only 44% of children with a Jewish mother and non-Jewish father were brought up in the maternal faith; and in couples where only the father was Jewish, the percentage fell to 10%.

One really sensitive question is this. To what extent is British Judaism's relatively conservative profile, and slightly increasing size, a reflection of the haredim or ultra-Orthodox Jews and their extremely high birth rates? As a colleague has written, the haredim account for less than 15% of the total Jewish population, but about a third of Jewish children under five come from that background. By the end of the century, the haredim could form a majority of British Jews. So is the statistical propensity to "marry in" and raise devout families a mainly haredi phenomenon? No or at least not yet, concludes Mr Graham. He notes that you if strip out the parts of London where most haredim live, the percentage of Jews who "marry out" is only a couple of points higher. But as time goes on, the community as a whole may start to look strikingly conservative, even if some parts of it live very liberally.

On his retirement in 2013, the former British and Commonwealth chief rabbi, Lord Jonathan Sacks, made the controversial statement that the future of diaspora Judaism was overshadowed both by assimilationist liberals and by ultra-conservative introverts. "The two fastest growing elements in the Jewish world are those who embrace the world and reject Judaism and those who embrace Judaism and reject the world," he said. As an observation about demographic trends in Britain, the latter point is hard to contest. But for the time being there seem to be plenty of Jews in Britain who are walking a line somewhere between the two polarities which worry the rabbi.