You don't venture into the Algiers casbah without protection and we make our way under heavy escort through a warren of over-populated back streets, souks, courtyards and winding alleys that seem to lead nowhere. Despite the area being declared a Unesco world heritage site, the crumbling colonial façades have seen better times and the pungent smell suggests that the plumbing system collapsed long ago. Attempts at regeneration have been slow and haphazard, hampered by the district's fearsome reputation in recent years as a terrorist recruiting ground.
Yet it was not always so, and eventually we arrive at the corner of a run-down cobbled street where, inside a small barber's shop, a framed but fading photo on the wall contains the evidence. Taken more than half a century ago, it depicts a group of smartly dressed musicians of various ages and ethnic origins – and it is here that the El Gusto story starts.
"I was in the shop one day and was intrigued by the picture and so I asked about it," says Safinez Bousbia, a 23-year-old Algerian film director, now resident in Dublin. "They told me that it was a group of Muslim and Jewish musicians who used to play in the cafés and at weddings and other ceremonies in the casbah. Before the war of independence, Jews and Muslims resided together in the same religiously diverse community, sharing the same lives and making music in common. I decided to find out if any of them were still alive and if they were to track them down."
Unsurprisingly, Bousbia's researches revealed that many of them were dead and that the Jewish musicians were long gone, having joined the 140,000 Jews who fled to France in the early 1960s – along with the French pieds noirs colonists – at the end of the war of independence. The new Algerian constitution enshrined Islam as the official state religion and outlawed public assembly for purposes of practising other faiths, and so with France offering them citizenship, they felt they had little option but to leave their homeland for good.
But some of the musicians had survived, both in Algiers and in France, and in several cases, their offspring have continued the family musical tradition. Bousbia also discovered that the group had been called El Gusto (it translates loosely as "the good mood") and had been formed at a famous music school run in the casbah by the acclaimed master and originator of modern Algerian chaabi music, Hadj El Anka.
El Anka had long since died, but Bousbia tracked down his son, the chaabi musician Abdel Hadi Halo, and together they located some 40 musicians, all of them over 60 and some as old as 90, living in France and Algeria. In November 2006 they bought them together in Algiers for a reunion concert, to record an album produced by Damon Albarn and to shoot a documentary film.
At least, that was the plan. In the event, the elderly Jewish musicians – none of whom had returned since 1962 – were too nervous to make the journey to Algeria. Thus the first reunion concert at the Algiers Opera House featured only Muslim musicians. So, too, does the album produced by Albarn.
Yet that wasn't the end of the story. Bousbia and El Hadi were both determined to realise their vision of reuniting the group and if the Jewish musicians wouldn't travel to Algeria, they laid plans to take the Muslim musicians to Europe instead. Their first concert together in more than 45 years took place triumphantly in Marseilles earlier this month and they will reunite again for a further performance at London's Barbican Centre of 10 October.
The mood in Marseilles is both nostalgic and electric with anticipation. "Music brought us together, history tore us apart and now we're back together," observes the 64-year-old Algerian-born Jewish singer Robert Castel. Now a well-known comedian and film star in France, Castel is the son of Lili Labassi, one of the founders of chaabi music whose songs are a central part of the El Gusto repertoire. "I began playing chaabi music in Algeria when I was four," says Castel. "My father worked with Jewish and Muslim musicians. He didn't see any difference."
Castel, who left Algeria when he was 29 in 1962, sees the El Gusto project as an important bridge between the now divided religious communities. "In the concert you will see an imam and a rabbi singing together. There is no racism and singing these songs of my father with Muslim musicians is getting back to our roots for me. There are no frontiers. That's what music can do."
The internationally acclaimed Jewish pianist Maurice El Médioni, whose album Descarga Oriental with Roberto Rodriguez won the boundary-crossing category in the BBC Radio 3 awards for world music earlier this year, also left Algeria in 1961, at the age of 34. "I was invited to play in Algiers last year but the time didn't seem right," he admits. "I don't want to talk politics, but I left because of the war and there were too many problems to go back. But when I told them I didn't want to go to Algeria, they said: 'All right, we will come to you.' I started playing chaabi music in the 1950s and back then it was natural for Jewish and Muslim musicians to perform together, so I was happy to be part of the project."
So what is chaabi music? "It really just means 'popular'," Abdel Hadi Halo explains. "Chaabi is to Algeria what rock music is to the West. It had its roots in Andalucian music brought to Algeria when the Jews and the Muslims were expelled from Spain 500 years ago, but my father started the traditions of modern chaabi after the Second World War. It grew up in the casbah and it has elements of Arabic, European and Jewish music.
"Before 1962, we all lived in the same community and played together. But after independence it became very difficult as the old Algeria splintered. It took us three years to track down all the musicians and put the orchestra back together."
Chaabi songs are typically drawn from everyday life and cover the gamut of human emotions – about pretty women, about pain and misery and nostalgia for the good times, with titles such as "Alger Alger" and "Les Pieds Noirs". It can be played by small ensembles but the El Gusto orchestra is a grand-scale version of some 40 musicians playing violins, ouds, guitars, banjos, cellos, flutes, accordions and traditional percussion fronted by no fewer than a dozen ancient but sturdily voiced lead singers.
Halo hopes to make a new recording which features both the Algerian-based Muslim musicians and the Jewish exiles. But for now we have the album featuring the Muslim musicians produced by Albarn in Algiers last year. "Yes, it's a shame the Jewish musicians didn't come," the Blur singer told me last November in a break between the recording sessions in a makeshift mobile studio on the top floor of the city's dilapidated Conservatoire overlooking the harbour. "But you work with what you've got and I think it's a really raw and authentic representation of chaabi music."
Albarn, however, was modest enough to talk down his own role. "When I was asked to get involved I did a lot of research into chaabi music, but there wasn't really a lot for me to do," he admitted. "It's mostly first takes because they're master musicians and we've done the whole album in two days."
A year on, in Marseilles, Halo has the last word. "There is no star in the El Gusto story because everybody is a star," he says. "We hadn't met for many years, but we came back together to sing chaabi because the music unites us."
El Gusto play at the Ramadan Nights Festival at the Barbican, London EC1 (020-7638 8891) on 10 October; the album 'Abdel Hadi Halo and the El Gusto Orchestra of Algiers' is released on Honest Jon's Records that weekReuse content