The Truth About ViolenceMost people think of themselves as calm, peaceful, law-abiding creatures. But could anyone be driven to kill another person? To pull the trigger and end a life? The Truth About Violence discovers the terrifying violence that lies within everyone.

Violence is part of everyday life - from knife and gun crime to war. But surely ordinary people could never be capable of a heinous crime? Self-proclaimed calm and peaceful Michael Portillo is set to find out.

Portillo says he has never been in a fight and doesn't have a single aggressive bone in his body. "I was brought up to try to resolve all conflict peacefully. I can't associate with violence. I don't understand how any human being can take violence to the extent of taking another persons life. I want to understand what makes people violent, what drives people to do it."

The brain chemical serotonin plays a key part in people's ability to control their aggression. Low levels can cause individuals to become violent, and it's surprisingly easy for this to happen. Sleeplessness, for example, lowers a person's levels of serotonin and impairs their brain's ability to function properly, leading them to potentially commit sudden acts of violence.

Brain damage, from mild concussion routinely received in contact sports, is also a significant cause of aggression. But this isn't a minor problem affecting elite athletes. Sixty per cent of wife batterers tested by Dr Golden, from Nova Southeastern University in Florida, had brain damage - damage that could have occurred at any time, without them even knowing it.

This is just a preview.The full documentary is not available at this moment.