You could be forgiven for imagining that a holiday in Rio de Janeiro involved stretching out on Ipanema beach, trekking up the Sugar Loaf mountain or attempting to dance the samba after a bellyful of caipirinha. This week, however, another attraction was added to the list: posing for photos alongside teenage drug traffickers clutching Russian machine guns and bags of Bolivian cocaine.

Rio’s tourist police are investigating after a Brazilian reporter went “undercover” on one of the city’s shantytown or favela tours. He claims to have witnessed the tour guide introducing witless gringos to a member of the drug faction that controls Rio’s largest shantytown, Rocinha, and then watched as they posed for photos.

There are around 600 redbrick favelas in Rio de Janeiro, home to around a million of its poorest people. The slums are considered no-go zones by most Brazilians. Foreigners, however, have always shown more interest in Rio’s impoverished underbelly. Since the 1980s, when guidebooks suggested cunning ways to sneak a peek at the favelas without actually going in, “poorism” has been a growing trend. Within a few years tour companies began offering visitors the chance to talk to locals, visit social projects and buy art from “authentic” (ie dirt poor) Brazilians. Today a new, less savoury, generation of “poor guides” has sprung up. For around $60 a head, they offer to transport thrill-seeking foreigners into a real-life version of City of God, the acclaimed film about Rio’s gang culture.

Some years ago I was approached by a dishevelled-looking North American, who described himself as an “alternative tour guide”. He claimed he was taking a young English couple to meet some gangsters. Would I like to come?

The next day, we were led up a steep concrete staircase towards the top of a shantytown in Copa-cabana. Halfway up the hillside we stopped to chat with a pair of traffickers and for the guide to fill his nostrils with cocaine. I asked the guide if he didn’t think the tours a tad over the top. He shook his head wildly, a thick white ring now etchedaround his nostril. It was important, he pontificated, for tourists to know the “real Rio”.