Stretched across the looms are lines of threads, bright pinks, reds, greens. The weavers are busy making beautiful, intricate silk saris.
But some of those weaving the fine, expensive cloth are
modern-day slaves. Ashok Kumar is one. He is a small, slim boy of 13, busy making delicate patterns in real gold thread along the borders of the sari.
Ashok says he has been weaving since he was nine. He sits working for 12 hours every day, seven days a week. He gets just one day off each month. He is a bonded labourer, what is also known as a debt slave.
When Ashok's mother died, his father left home. The boy was abandoned with his grandmother. Desperate for money she took £12 ($25) from a loom owner and, in return, sold the boy's freedom.
Ashok is now bonded, forced to do this one job. He is not free to leave unless the debt is repaid. And he is paid just 15p (30 US cents) a day, so there is little hope he will ever do that.
Ashok's boss, Muthu Pereumal, can sell the boy to another employer, trade him like a commodity. 
"He will stay here until he is 20 or 22," the boss tells me, standing by Ashok's loom, "or until someone else comes to buy him from me. He will never do anything else but this."
"Because the families are so poor they will give me a child who will work for as long as I want," Muthu Pereumal says.
"In return, we give them an advance of up to £60 ($100). Adults cannot afford to work for such low pay. Without children working like this it would not be possible for our industry to survive." 
Kanchipuram, Ashok's hometown in southern India, is built on the silk industry.
Sixty thousand people work making the town's famous saris. The local labour union estimates 12,000,
one in five, are bonded labourers.They are also used in many other industries from leather-making to road-building, agricultural labour to silver work. Campaigners say there could be from
10-40m bonded labourers in India. Away from his boss, Ashok is willing to talk about the awful conditions he endures.
"Because I work at the loom my hands hurt. Sitting for a long time gives me pains in my back," he says. 
"Sometimes I get headaches and my eyes hurt. But I have to keep going until eight in the evening. Only after that can I go home and sleep."
Far from Kanchipuram, traffic rumbles along Tooting High Street in south London. Britain abolished the slave trade 200 years ago, but products from industries that use slave labour are still sold here.
In his shop, Raj Siva is unpacking Kanchipuram saris. South Indians prize the intricate handmade silks as wedding dresses.
They fetch up to £900 each in the UK.
