Hampstead Garden Suburb Synagogue is a byword for genteel respectability, zealously guarded by its inhabitants. The kind of neighbourhood where every bush is trim and no brick out of place. So the local United Synagogue, too, you might imagine would be a bastion of conservatism, the eptiome of the decorous traditions of Minhag Anglia. Certainly not where you'd expect people to go dancing around the bimah on a Friday night.

But that's exactly what you may find at HGS from time to time. Since he arrived there last year from Caesarea, American-born Rabbi Dov Kaplan has been trying to lighten the congregational style, introducing a little more simchah, joy, into the services.

Over the past couple of decades, there has been a gradual shift in many synagogues where the choral operatics of 19th century composers have given way to the singalong neo-Chasidic niggunim of Rabbi Shlomo Carlebach. Once associated with the countercultural 1960s, Carlebach's catchy numbers have become standard shul fare, as well as other contemporary tunes from Israel and America.

HGS is one of the diminishing number of synagogues that retains its own professional chazan with the capability to do the classical repertoire, the respected Avromi Freilich. But he has proved amenable to introducing more contemporary melodies.

"There are people in the community who didn't like the Carlebach," Rabbi Kaplan said. "But I think we brought them round to realise that if you want the next generation in, and not staying at home or looking elsewhere, then we have to move with the times within the boundaries we are allowed to."

But Rabbi Kaplan has been prepared to push the musical boat out a little further. Every he so often he goes for what he calls a "full-blown" Carlebach service, with more singing, hands clapping or drumming tables, and even a spin or two around the bimah.

To get people on their feet, he has had to overcome some native reserve. "If I start dancing with two of my sons and others who have been with us in Caesearea, I have to go and drag people into the aisles to dance with us," he said. As the circle expands, others gradually feel emboldened to join in.

At its peak, the service has attracted a few hundred worshippers. "The first-time we did a full-blown Carlebach Friday night, I thought the place was jumping. I thought the service had gone really well, everyone was smiling," he recalled. "One of the older, respected members came up to me and said, 'Rabbi, I just wanted to tell you, I have never seen something so disgusting in shul!'"

But Rabbi Kaplan admits that he himself was initially resistant to the appeal of Carlebach. "My older brother who is a doctor, wasn't pleased with the shuls where he was living," he said. "He got together a small group of friends and they tried one Friday night Carlebach. The next week, they doubled the numbers. The third week they didn't have room for everybody. Theirs is now probably the largest, most successful Carlebach synagogue in the world, located near Bar-Ilan University."

It took a spell with a congregation in Colombia to convert Rabbi Kaplan. "We found a very sleepy shul that was badly attended," he said. "My brother made a recording of Carlebach, sent it to me and I learned the tunes. We tried it and it made all the difference. People started coming. From then on, I realised, there was no looking back, most people like this."

While synagogues should maintain "a certain decorum", he said, "that should not detract from us coming there to be happy Jews. During the Jubilee Week, I was standing on the embankment, waiting for the Queen and her entourage to come by. There were people from all different races. I had my kippah on and so did my sons. People were standing shoulder to shoulder and they were happy.

"We should be happy to be Jews. But where can we show our happiness? That's in shul. When we come to shul, it has to be expressed."

Other rabbis, too, have found change pays off. After Rabbi Leo Dee came to Radlett United Synagogue last year, he introduced a regular, full singing, dancing Carlebach Friday night service, seeing numbers more than double. "For an extra five or 10 minutes [longer than the traditional service]," he said, "you can make it fun. We have families that come every Friday night with their kids."

In winter, Radlett's service now starts at six o'clock rather than the onset of Shabbat, which has proved to be a more family-friendly time.

Raising Friday night attendance is a particular ambition of his Rabbi Dee - and that can make an s impact in the long run.

He recalls someone telling him that "on his first Friday night at university, he went to the J-Soc [Jewish society] but he felt uncomfortable and didn't recognise the service, so instead he spent every Friday night at the bar.

"Going to Friday night services is something important we can do as parents for our kids. If they feel comfortable there, then the natural place they will end up at university on a Friday night at university is at J-Soc."