More than a decade ago, Amar was seriously injured: his leg was infected and his family couldn't afford the treatment required to save the limb. It looked like he would lose his leg, for the price of a lunch every day.

Then there's nine-year-old Vijay. He was found lying in the great Howrah railway station, where he slept with a razor blade under his tongue. He used the blade to defend himself from attackers. Yet most of the time he ended up slashing himself to ribbons.

And how about 12-year-old Abhik? He was burned quite hideously when his mosquito net caught fire: a fire that killed his mother, who was lying next to him. He was also found in the station, sniffing glue and smoking heroin.

And then there's 15-year-old Dinesh. He was discovered at the age of seven, living on the streets, having been continuously raped for years by predatory homosexuals: his syphilis was so bad he had to sit on a bucket of potassium permanganate for six weeks.

Where are we? Kolkata, of course: that great, majestic, troubled and teeming capital of India's West Bengal, formerly known as Calcutta. This is the city of Mother Teresa and her beggars and lepers. This is the so-called 'city of joy'. This is the city that provoked Winston Churchill to say: "I am glad I have now been to Kolkata, as it means I never have to go there again."

A nightmare of poverty and suffering
And yet, if Kolkata can sometimes seem like a nightmare of poverty and suffering, it still has many beacons of optimism: and one of the very brightest is Futurehope, a charity for homeless children run by an affable fifty-something Englishman, called Tim Grandage.

'Tim Uncle' as he is known to his co-workers and charges, spends his time rescuing waifs and strays from the pitiless streets of the Bengali slumopolis. Dinesh, Vijay, and Abhik have all, for instance, found a home with Futurehope. This is why we know their appalling stories - though their identities must be disguised - to protect their future prospects.

But 'Tim Uncle' doesn't just rescue and feed his charges. He teaches them to live, learn and laugh like normal people, to lead a constructive existence. And one of the main techniques he uses, when rehabilitating the youngsters, is sport, especially team sports like football.

Sitting on the sun-drenched balcony of a Futurehope kids' home, Tim takes up his remarkable story.

"I was working for HSBC in Kolkata. I was a young man, a bachelor boy, leading a fairly aimless existence. One day I was watching some kids in the street: it was monsoon time, the streets were literally flooded. Waist-deep in muddy water. All the guys at the bank were complaining, of course. But these kids they were swimming in the rainwater: laughing, playing, celebrating. It really affected me. I'm not sure why."

Soon after that. Tim happened upon another streetchild, who was desperately ill. Appalled at the child's condition, Tim took the boy to a friendly doctor. The physician readily agreed to help.

Gave up his banking career to help street kids
Without such generosity, the boy would likely have died. Tim and his doctor friend had saved a life. The experience gave Grandage the kind of emotional buzz you don't get from corporate loans: within a few years he had given up his banking career, and set himself up as a full-time charity worker.

It wasn't easy at first. Tim's company, HSBC, were "incredibly understanding and generous" - the bank funded Tim's endeavours, and provided many other resources. Nonetheless, in the early days, things were extremely primitive. At one point Tim was living with 32 street kids in his own two-bedroom apartment. Everyone slept on the floor. He keeps the photos to prove it.

Two decades on, Tim Grandage's Futurehope is a very different concern. Acclaimed around the world for their work, the Futurehope dormitories sleep at least 200 homeless children every night. The Futurehope schools teach the children art and maths, music and English. More kids come in from the slums as 'day scholars' - children who aren't technically homeless, but who would otherwise go without schooling. "There are reckoned to be 100 million illiterate children in India", says Tim. "And 100,000 are homeless in Kolkata alone."

It's a daunting task. But the rewards - spiritual and emotional - are huge. Tim and his co-workers can really make a difference, as we are about to found out, during our visit to the Maidan, the great central space at the heart of Kolkata.

When we arrive at the Maidan, a bunch of Futurehope footballers are already there; having a playful kickabout. The referee is a charming teenager with certain mental problems: but no one seems to care. More than a few kids have the most challenging backgrounds: born of teenage prostitutes, or afflicted with psychological conditions, or getting over a life of drug addiction - that may have begun at the age of six.

'People sneer, the police beat you up'
Yet here they are: just another laughing football team. Jagdeep is a slightly older boy who has come through the Futurehope system. He explains a further advantage of football, and other sports, in the childrens' lives.

"It makes us realise we can win," he said. "When you are homeless, you are a loser. OK, you are free and there's no school, and that's maybe fun when you are eight, but as you grow older you realise everyone looks down at you. People sneer, the police beat you up. But then you join Futurehope, and you get in the football team."

Jagdeep smiles: "And then maybe you play the police team and you beat them. We do that regularly! That is a very good feeling. Believe me! And then the police learn to respect us, and we learn to respect ourselves."

As the warm winter sun goes down, over the grandiose Victoria Memorial, Tim takes us on a tour of the City of Joy. We go to the shores of the great river Hooghly, a tributary of the Ganges, where thousands of men are washing in the filthy water. Further down the shore: corpses are being burned, in great open funeral pyres. Death is never far away in Kolkata.

Then we make the journey to the vast Howrah railway station: where so many of the Futurehope kids are discovered.

Lying across the tracks
Almost the first thing we see is a teenage boy, lying across the tracks, with a green flannel draped over his face, the flannel is soaked in glue. The boy spasms as he inhales the solvent.

Tim crosses the tracks, and approaches the boy. For Tim Uncle there is always another streetkid to be rescued. And, who knows, maybe another recruit to his remarkable football team. And Tim wants to find recruits, because he knows that if he can get the kids at the right time - then he can transform their prospects.

The guy driving us back to the children's home is a fine example. Because it's Amar. When Amar came to Tim with his wounded leg, Tim and his wife, a nurse, took Amar into their home. Tim's wife changed the boy's dressing every day. Now Amar is a healthy and happy young man: he is heading for Kurdistan next month, to work for a large corporation. Such an outcome would have been inconceivable without Futurehope. As Amar himself phrases it: "I don't know what I would have done without Tim Uncle. I don't even like to think about it."

Amar is more loquacious on the subject of football - and the role of sport in Futurehope. "Tim always gets the kids to play team football, boys and girls alike. Often the children are very good, because they are so competitive. But they have to learn team spirit. To co-operate. That's not something you learn when you are living under station platforms, with rats. And the sports keep the kids fit and engaged, and it gives them rewards for working hard. And that can really save lives." As we drive into the brightly painted compound of the chilren's home, Amar smiles, almost wistfully. "You know, there's a reason the charity is called Futurehope."