Almost a million people live in Kibera, Africa's biggest, dirtiest, poorest slum. It's in a narrow valley tucked away on the edge of the Kenyan capital Nairobi - a world away from the beaches and safaris the tourists see. In the first of two talks, Andrew Harding meets the muggers, the vigilantes and the children struggling to survive in a vast maze of mud and poverty. Producer Sue Ellis Repeated Saturday 7.45pm