The new research shows that while marriage between Jews and non-Jews is at a record high of 26 per cent, it has climbed by only one per cent since the mid-1990s. This compares with a figure of 58 per cent for the United States.
Whereas 96 per cent of Jews who married-in raise their children as Jewish, only 31 per cent of intermarried couples do. And while 44 per cent of intermarried Jewish women raise their children as Jewish, just 10 per cent of intermarried Jewish men do.
The intermarriage rate has more than doubled since the end of the 1960s when it was 11 per cent. It hit 23 per cent in 1980-4 and has stood at around one in four since 1995. The previous high was 25 per cent during the 1995-9 and 2005-9 periods.
Ephraim Mirvis, the Chief Rabbi, said that the report had a "clear" message. "This report brings into sharp focus the stark reality that levels of Jewish attachment, religious observance and continuity, directly correlate with what it calls 'endogamy' – marrying in," he said. "The message for our community could not be clearer. It is pleasing that the increase in intermarriage has been extremely slight over recent decades, particularly in comparison with the United States. But we must never be complacent. On the contrary, we must redouble our efforts to cultivate the Jewish pride and identity of our children so that they appreciate the eternal value of our heritage."
Dr Graham, whose report, Jews in couples, is based on "the widest collection of data" on the subject in the UK, taken from the 2011 National Census and JPR's 2013 community survey, said that intermarriage, was "demographically corrosive".
He explained: "This is because expansion depends on the assumption that the children of intermarried Jews share the same level of Jewish commitment as the children of in-married Jews. But this is empirically not the case."
Overall, 22 per cent of the Anglo-Jewish population has a non-Jewish spouse, while that goes up to 28 per cent if cohabiting couples are included. Those who are in their early 40s are the likeliest to be intermarried.
Rabbi Daniel Rowe, executive director of Aish, commented: "It vindicates what we have been saying for a while, that the investment of the past two decades across the community has borne fruit and that in many ways, British Jewry can help serve as a model for other communities in the breadth, depth and effectiveness of identity and continuity-focused projects."
However, Rabbi Aaron Goldstein, of Northwood and Pinner Liberal Synagogue, said the research raised its own issues.
"Surely, the figures say as much about how the Jewish community treats such couples as it does about the attitudes of the couples themselves?" he asked.
"If we treat people with disdain, then it is hardly surprising that they choose to opt out of our community. But if we welcome such couples, then we massively increase the chances that intermarriage means marrying in, not marrying out. That is the experience and practice of Liberal Judaism."
Dr Graham, who is a senior research fellow at the JPR added that, although intermarriage had been a concern within the community for 50 years, "this report suggests that British Jews are managing to get the balance about right, indicating that the Jewish community should be considered an exemplar to others about how to maintain a distinctive and particular identity in a modern multicultural society".
While intermarriage seemed "unlikely to engulf the community any time soon," he said that there were "well-grounded concerns" about the prospect of the children of intermarried couples being raised as Jewish.
Compared with Jews who married in, he found that "intermarried Jews produce fewer children, are one-third as likely to raise their children as Jews, are twice as likely to get divorced and at least twice as likely to have intermarried children themselves."
Jewish couples also have more children on average, 2.4 per couple, compared with the 2.1 of intermarried families.
The research also showed that Jewish divorce has risen from eight to 11 per cent over a decade, while one in six Jewish adults - 17 per cent - has been divorced. Three-quarters of divorcees who had a Jewish wedding obtained a get.
The Jewish divorce rate of 34 per cent since the 1980s is lower than the national average of 47 per cent. Jews who remarry are two and a half times as likely to marry out than Jews who are marrying for the first time.
Cohabitation is also on the increase but fewer than one in three cohabiting Jews have a Jewish partner. The rise in cohabitation and the fact that women are marrying later have also led to lower Jewish birthrates outside the Charedi community.
Since a third of young Jews aged from 25 to 29 in a couple are living with their partner rather than married, cohabiting could become "an increasingly central factor in communal life," the report suggests.
The report also explores the topics of divorce, cohabitation and same-sex couples, and shows that Jews today marry seven years older than they did in the 1970s, with the average age for a groom 32 and a bride 29 (compared with 32 for men and 30 for women in the general population).
On average, Charedi Jews marry at 23 and Orthodox at 25, whereas secular Jews who marry are nearer 30.
Just under two per cent of Jews in couples are in a same-sex relationship.
Overall, Dr Graham concluded, "the traditional picture of Jewish married life remains robust in Britain". He added that Jews are currently "more likely to live in a couple than any other religious or ethnic group", fractionally ahead of Christians.
Senior rabbi to the Reform movement Rabbi Laura Janner-Klausner said: "This is a moment for celebration as our concerns have not come to fruition. We have ensured that people of all backgrounds can flourish in our communities thanks to our inclusive attitudes. And now our challenge is to continue to inspire Jewish life with flourishing synagogues and homes."
