The odours meander from the faint stench of rotting fish to the reek of human waste – not quite what should be expected from one of the season’s hippest holiday destinations.

But Mumbai’s controversial “slum tourism” industry, which promises fee-paying outsiders a glimpse of life inside the city’s shantytowns, is flourishing. Numbers are up, agents say, as Westerners shun the beaches of Goa and palaces of Rajasthan to experience the reality behind British film Slumdog Millionaire.

“Everybody is talking about Slumdog,” said Ganesh Tikonkar, a guide for Reality Tours, a company that takes about 50 people a day through Dharavi, Asia’s biggest slum. “Now people want to see the real thing.”

In their quest for the truth Mr Tikonkar’s clients spend three hours following him through one of the world’s most densely populated neighbourhoods, soaking up the fetid atmosphere and learning about a vibrant intra-slum economy worth an estimated £700 million a year.

Along the way they pass through the factories that recycle Mumbai’s waste, leather tanneries that supply the likes of Gucci and one of the biggest poppadum-making operations on the sub-continent. They venture deep into an area many Mumbai residents will never visit: a heartshaped warren of rusting tin, open drains and dark alleys that covers a square mile in the centre of the city and is home to a million people. The terrain forms the backdrop of Slumdog Millionaire, which tells the story of Jamal Malik, a dirt-poor orphan from the slums who astonishes India when he does well on the country’s version of Who Wants to be a Millionaire?. While the show offers Jamal a route out of the gutter, the tour makes a beeline for the squalor from which his real-life equivalents strive to escape: the excursion’s “highlights” include a stop at a stall of six toilets that serves 16,000 people and a stroll alongside a river so black and septic that it oozes rather than flows.

“The movie is a fairytale. This trip shows things are a little darker, a little grittier in reality,” said Bill Alves from Seattle, who is retired and went on the tour after seeing the film.

The Dharavi expedition is part of a new tourism that is gaining traction across the developing world. Operators have begun leading curious, rich Westerners into famous slums, from the townships of Soweto to the favelas of Brazil. “The jury’s still out on whether the tours are perverse invasions of privacy or eye-opening experiences that will prompt action on the poverty agenda,” Christine Bowers, a consultant for the World Bank, said on her blog.

Advocates say that the Dharavi excursions help to illuminate the slum’s qualities and benefit their inhabitants. “Yes, these places have their grim side, but many people who go on the tours are surprised to find thriving, diverse communities, who live together peacefully,” Deval Sanghavi, of Deval, a Mumbai-based NGO, said.

For his part Mr Tikonkar, of Reality Tours, marshals his clients closely; photographs are not allowed and 80 per cent of his company’s profits are spent on social schemes in Dharavi.

One thing that eager tourists should not expect is the chance to quiz the inhabitants on their impressions of Slumdog’s veracity: despite the series of awards the film has won, virtually nobody in the slum has heard of it.

“We don’t know it and won’t go to see it,” said Priyanka, 12, as she carried her little brother Ram, 4, on her hip. “We only like films with Shah Rukh Khan,” she added, doing a twirl at the mention of Bollywood’s biggest star.

Many onlookers initially felt that the film, which premieres in the country on Thursday, would prove too edgy for conservative audiences found outside India’s big cities.

Yesterday the director Danny Boyle insisted that the film’s reception in India was crucial. Asked if he expected any Academy Award nominations, declared tomorrow, he said: “The most important thing for us this week is absolutely the opening here.”

Times Recommends

• Please help: maimed children of war want their lives back
• Cabal seizes diamond riches to buy power
• White House gatecrashers got to the president