Where are the great kosher restaurants?

Paris also sustains hundreds of high-quality kosher eateries.

"There are 30 sushi restaurants alone" says kosher caterer Adam Zeitlin of Zeitlin & Co, a regular visitor to Paris. "There is a wider range of good, kosher food there. The patisserie is wonderful - there is simply no comparison here."

A French businessman has invested €600,000 in creating Rafael, a new kosher haute cuisine establishment headed by chef Simone Zanoni, previously head chef at Gordon Ramsay's Paris outpost, Trianon Palace. Zanoni has plans for a Michelin star and has similar aspirations for a New York venture - for which he has managed to secure $100,000 from a New York businessman. The situation is starkly different here. Of the 30 or so kosher restaurants in our capital, only two - Zest and 1701 - could entice serious food critics.

Zest, part of JW3 on Finchley Road, did have Giles Coren and Jay Rayner (both Jewish and perhaps the harshest critics of their own culinary heritage) dancing merry jigs up the Finchley Road. Rayner wrote: "Quietly, unexpectedly - and without anybody bothering to consult me - Jewish food has become really, really good. Frankly, I'm appalled."

Yet, although head chef Eran Tibi's food is as good as any to be found at Ottolenghi's outlets, Raymond Simonson, JW3's CEO, estimates that only about 15 per cent of Zest's diners are non-Jewish.

This is nothing new. The few attempts at a higher standard of kosher fare have all bitten the dust. The cavernous and now defunct Six-13 on Wigmore Street was heavy on confits and jus but light on customers, as was the upmarket Brasserie 103 in Golders Green.

Most recently, 1701 at London's Bevis Marks Synagogue, despite a mention in the prestigious Michelin Guide, closed its doors.

Owner Lionel Salama, who plans a West End relaunch, acknowledges his audience is limited: "Ours is not a particularly big community and, within it, fewer and fewer people eat kosher out."

The size of the kosher-keeping British community is relatively small. Institute of Jewish Policy Research (JPR) figures state that 300,000 Jews currently live in the UK (200,000 in London or its environs) and only 27 per cent of them eat only-kosher meat out (JPR's 2013 NJCS).

Salama points out kosher eateries also face other financial restraints: "Being closed on Friday nights, Saturdays and most Sundays for synagogue functions meant that we only had eight meal services a week."

On top of this, the additional cost of supervision and of buying kosher ingredients, can add 20 per cent to a restaurant's outgoings.

Nick Lander, restaurant correspondent at the Financial Times and consultant for JW3's Zest says: "It is not just the cost of supervision, but the raw ingredients and, most surprisingly, dairy. This means that even the most basic items on a menu, coffee, tea etc, do not generate the same gross profit as in a non-kosher restaurant - unless the sales price is higher. But these are the first things people compare and indicate that kosher equals expensive."

So why would a sane business person take on the additional burden of kosher when the restaurant business is already littered with failures?

A much-bandied about survey by Ohio State University claims that as many as 60 per cent of restaurants don't get past one year of trading.

Yet kosher restaurants thrive in New York and Paris, where religious restrictions remain the same.

New Yorker Tamar Genger, online editor of Joy of Kosher, explains there are several tiers of kashrut in the US. Some of New York's restaurants, often run by non-Jews, trade under the more lenient licensing bodies, which allow them to trade on Shabbat. So perhaps not the same rules everywhere, but many New York eateries do observe the more strict religious requirements.

Another key difference between the US and here is the perception of the hechsher, which is seen there as aspirational.

"In America, the US OU (Orthodox Union) hechsher is seen as a quality mark," explains Lance Forman of Forman & Co, whose smoked salmon needed a hechsher to sell in the US, but who has found it less attractive to customers in other territories.

"In Israel, a kosher licence can be perceived as a negative - if it's kosher it can't be very good" explains Forman.

Here the hechsher does not hold the same cachet, but Salama suggests kosher's religious connotations itself may be a barrier to a non-Jewish clientele. "When we removed the 'kosher' signage at our counter at Selfridges and rebranded it 'Adafina' the sales went up. Kosher creates a little ghetto - people won't come and try it," says Salama.

There also has traditionally been a lack of interest within the wider Jewish community. Raymond Simonson recalls growing up in Redbridge in North-East London: "It was the most densely populated area of the capital with almost 18,000 Jews but there was only one kosher restaurant, The Sharon, which closed in the late 1980s. When it closed, it was replaced by a kosher-style restaurant serving salt beef and latkes, but no kosher restaurant, as no one could sustain one there."

We have also not been that demanding of our kosher restaurants. "They are not on a standard of say, Nobu, or other fine dining, but I don't think people expect it or want it", suggests Forman.

Simonson agrees: "We've all come to expect a certain sort of kosher restaurant because no one has challenged it." The most obvious reason for the greater breadth and standard of kosher eateries in New York and Paris could be financial. With New York's Jewish community numbering 2.1 million, even with only an estimated 32 per cent of them keeping kosher, there are just that many more bums to go on seats.

According to Anne Shooter, author of Jewish baking book, Sesame and Spice, who works in both London and New York, the culture is also different: "It just seems to me that New York has a larger observant Jewish population and can therefore sustain more restaurants. Also, Jewishness is so much part of what the city is about that everyone eats Jewish food, not just Jews, so there's a lot more of it, kosher or not."

In Paris, the community isn't much larger than London's, at 283,000 but there were still close to 300 kosher restaurants at the end of 2013. The general consensus is this is down to customer demand.

"French Sephardi Jews are more observant and many prefer to eat kosher when out than they do dine out," explains London cookery teacher and food writer, ex-Parisienne, Fabienne Viner-Luzatto.

And unlike here, where kosher restaurants tend to be contained within the residential ghettoes, in Paris and New York, kosher restaurants sit alongside mainstream restaurants. Non-Jewish diners clash elbows with kipah-wearing folk.

But Zest is not the only light at the end of the kosher dining tunnel. Many high-end kosher caterers are keeping up with modern food trends in menus and presentation, and a series of kosher pop ups and supper clubs have brought kosher into the 21st century. It just leaves the restaurants to follow their lead.

"I think Blooms is one of the greatest missed opportunities in kosher catering. That place could have been heaving now if they had modernised for the 21st century," laughs Forman. He could be right.