By Justin Rowlatt

The world is suffering from an invisible epidemic, an epidemic of pain.

As many as 60 million people are reckoned to suffer avoidable agony every year.

It is a situation that a visionary Indian doctor, Dr MR Rajagopal, has been campaigning to change for decades.

It isn't that the patients themselves are silent, he explains. Indeed, it was hearing the screams of agony of a neighbour in the last stages of cancer almost four decades ago that first set him on the path that would earn him his nickname: India's "father of palliative care".

"His family asked if I could help", he says, "and I couldn't, I was just a medical student."

It was his sense of helplessness in the face of that suffering that led him to specialise first as an anaesthetist, then in palliative care - the prevention and treatment of serious health-related suffering.