In his role as the United Synagogue's 'Young US' Rabbi, Josh Zaitschek has a clear recipe for attracting young people to shul . "Social activity for those wanting to unwind and meet new people; business networking opportunities to support developing careers; social action and rewarding volunteering roles," are top of his list.

And there is more: "Food-related events for those who live to eat; residential trips to get away from it all with like-minded people; stimulating, sophisticated education in a relaxed environment; and, of course, access to meaningful spiritual expression with services to match."

Rabbi Zaitschek said these are the ingredients "for young people to feel a real sense of belonging" to their shul community. He added: "If you want to enjoy next year's Cholent-Fest, trips abroad, business leader seminars, spa retreats, restaurant evenings etc, you'll be visiting any of a number of venues which make up the larger virtual community designed to suit you.

"This is a healthy and creative way to be thinking about young communities.

"The model may look different to the traditional community, but the ethos that underpins it is not. Young and old, we are united by shared core values which we carry with us for life and look to pass on to future generations."

Young and old, we are united by shared core values

According to the rabbi, under-30 membership of the US stands at approximately 2,000, with roughly half of these belonging to its discounted young membership scheme.

At Reform Judaism, younger people are also provided with there own dedicated rabbi. For the last two years, Rabbi Benji Stanley has worked as the movement's first-ever rabbi for young adults.

"I want to emphasise the diversity of this generation," he said. "We often imagine that young people are somehow going to be less diverse than any other section of society but that's far from the case.

"Some of them are involved in synagogues or would like to become involved, while some of them are quite clear that it's not for them, at least not for now."

He added: "I think one of the strongest themes was that a lot of young people have come through our youth movements and they are very attached to a culture of participation, so often what they want is to learn to participate in a service, whether that's from the front or as a member of the community.

"My experience is that we underestimate the hunger of this generation for Jewish learning."

And shul also acts as a meeting point across the generations. Rabbi Stanley said: "Many young adults want to be in a space where they aren't just in an echo chamber. They like coming along to kiddish to talk to people who remind them of their grandparents."

Around 500 21-29 year-olds are signed up members of Liberal Judaism communities. The movement has a dedicated chaplain, Rabbi Leah Jordan, whose brief is student chaplaincy and young adults.

A spokesman said: "There is a general feeling that liberal progressive Judaism is more in tune with modern world - it attracts people with non-Jewish partners, and also patrilineality, so we think this adds to our success with young people."

At Masorti Judaism, chief executive Matt Plen says a large percentage of people who are joining its synagogues are young families.

But he added: "We are investing a lot of effort into building community events and community networks for people in their twenties outside of the synagogue framework.

"We have a young adults organisation called Marom with several hundred involved."

According to Mr Plen, "a more synagogue-related Jewish life" can be encouraged by specific community initiatives, such as the young adults' minyan, Ohel Moed, which holds Shabbat services and Talmud readings.

With the cost of shul membership recognised as a barrier for younger people, most Masorti communities offer discounts.

The S&P Sephardi Community is targeting this demographic with initiatives such as "Culture in the City" at Bevis Marks in the City of London, where monthly events and classes for young professionals are open to members and non-members.

Friday dinners and social events for young professionals at Lauderdale Road synagogue have been "hugely successful", a spokesman said.