The survey reveals striking evidence of the religiously squeezed middle.

While the traditional camp that typified the middle-of-the-road United Synagogue member has shrunk, there has been a significant rise in the numbers of Jews who identify as cultural or secular.

Almost half of those who were raised as “traditional” or “Reform/Progressive” have switched religious allegiance, some going right but mostly left.

So while some traditional Jews may now see themselves as Orthodox or even Charedi, most have gone towards the Progressives or seculars.

And while some Progressives might have moved to Masorti, for example, or further right, the trend of most of their movers, too, has been left.

“This switch away from traditional is suggestive of a shake-out of the middle ground,” the report states.

This is apparent if you compare how people were brought up with how they see themselves now.

The secular/cultural group has risen from 15 per cent to 24 per cent, the Progressives from 15 per cent to 18 per cent, the Charedim from three to four per cent. The Orthodox have retained the same proportion at 12 per cent. But the traditionals have slumped from 40 per cent to 26 per cent.

The trend towards secularisation “appears to be happening among older respondents to a greater extent than among younger correspondents,” the report suggests.

But then there is a disproportionately larger number of Orthodox and Charedi Jews among the younger groups than older groups.

If you look at the middle aged, 40-64 bracket, the share of the religious market held by traditionals, Reform and seculars is higher than among the under-40s: whereas the opposite is true for Orthodox and Charedim.

Five per cent of the sample said their current position was either none, mixed faith or other.

WHAT THE FIGURES MEAN

On first glance, the proportion of Charedim at four per cent looks far smaller than it ought to be — especially given data elsewhere about the growth of the strictly Orthodox population.

Almost certainly, some Jews who might be considered “Charedi” by others have described themselves as simply “Orthodox”.

Orthodox probably represents shomer Shabbat, while “middle of the road” Orthodox synagogue members might describe themselves rather as in the “traditional” camp.

Combining the Charedi and Orthodox groups gives an overall proportion of 16 per cent.

The figures represent religious identification rather than synagogue membership as such.

But the fact that the traditionals and Progressives have failed to retain almost half of their numbers is sobering for the United Synagogue and Reform.