Hectic: out and about on the streets of Delhi / AFP/Getty

A tour led by the capital's street children shows Harriet O'Brien a different side of the city

All life was crammed into the micro-lanes. Barely the breadth of the average person, the implausibly narrow alleys of Delhi's Paharganj district were lined with tailors, saucepan traders, one-man goldsmith workshops and mini cyber cafés overhung with washing. There was even a tiny garage mending motorbikes. As we snaked along, our guide, Tabrez, stopped beside an egg merchant who was precariously cooking in the path on a portable gas ring – a triumph of balance and spatial ingenuity.

I was on a walking tour of the backstreets near Delhi's main railway station, an offbeat excursion arranged by a charity for street children. I had visited the city's greatest sights on other trips: the remarkable Humayun's Tomb (precursor to the Taj Mahal); the majestic 17th-century Red Fort; lovely Lodhi Gardens and more. Partly through fear of getting lost, mainly through apprehension about what I would encounter, I had shied away from exploring the other-world of India's capital. But now, with a small group shepherded by Tabrez, I had turned off a leafy New Delhi avenue and plunged into a densely populated web where extraordinary enterprise helps to alleviate extreme poverty.

It was undoubtedly vibrant, but the scenes in the Paharganj lanes were rendered a sideshow as we became absorbed in finding out about the world of the street children. Twenty years before Slumdog Millionaire moved global audiences, another director, Mira Nair, brought the plight of India's homeless children to the world's attention with Salaam Bombay, a compelling film about street kids, acted by street kids. It was nominated for an Oscar and won three awards at the 1989 Montreal Film Festival. As we set out, Tabrez, a former street child himself, explained that with proceeds from the film, Nair and her mother, Praveen, set up the Salaam Baalak Trust, a non-profit organisation that supports street children through residential care, drop-in centres, healthcare and education. Since then, it has supported more than 50,000 children. In Delhi it operates five residential shelters and 11 day centres – and since 2005 it has organised city walks. Tabrez, now 20, trained as a guide just months before.

Tours start at Delhi's Rail Reservation Centre on Chelmsford Road. Every morning, workers bring children found newly arriving in the city to the charity's station office. The children get health checks and, if possible, are taken back home or to a shelter.

From here, the tour went to a backstreet refuge, via tiny bazaars, a potters' market, temples and video shops. Along the way, Tabrez paused to add intriguing insights. Around the corner from the egg man he pointed to a series of tiles along a wall, each painted with a religious symbol: the Hindu gods Ganesh and Vishnu, Christ and the crescent moon of Islam. "They've been put there to create greater sanitation," he told me. We were non-plussed. By putting up holy images, he explained, you effectively make a shrine that everyone respects. "Until recently, people used this lane as a latrine – but they don't any longer."

Collecting rubbish is a business for many street children. They are paid Rs30-35 (35-40p) per kilo of plastic. Basic survival is easy for street kids, Tabrez told us. They will always be fed at temples. But drugs, alcohol and inhaling adhesives are real dangers. Gambling too. All of which can lead to prostitution.

We entered the stairwell of a corner building and climbed to the fourth floor where a large apartment is now one of the trust's refuges for boys. Some had been painting; others were in a school room that doubles as a dormitory. They clustered around us, showing off and fooling around. Noticeboards outlined the achievements of recent leavers such as Nitish, who works for Delhi's metro, while Faizal pursues dreams of Bollywood and has acted in a movie.

Tabrez acknowledged, as he escorted us through the tangle of alleys back to the main road, that the trust helps only a tiny number. But it's been the saving of many – like him. We said our goodbyes; it had been a profoundly inspiring tour. And with that he disappeared back into the passageways, past a pop-up barber shaving his client in the open air.

Travel Essentials

Getting there

Harriet O'Brien travelled to Delhi with Greaves (020-7487 9111; greavesindia.co.uk). A three-night break including flights from Heathrow, transfers, a Salaam Baalak Trust walk and a stay at the Oberoi New Delhi, which supports Delhi-based charities, costs from £1,199pp. Delhi is served from Heathrow by British Airways, Air India, Virgin and Jet Airways.

Visiting there

Salaam Baalak Trust, New Delhi (00 91 11 23584164; salaambaalaktrust.com). Guided walks Monday to Saturday 10am-noon; contributions Rs200pp (£2.30).

More information

British passport-holders require a visa to visit India, which costs £92.20 for a tourist (0905 757 0045, calls 95p/min; in.vfsglobal.co.uk).