Forty years ago a group of students hoping to make a bit of holiday money turned up at a basement in Stanford University, California, for what was to become one of the most notorious experiments in the study of human psychology.

The idea was simple - take a group of volunteers, tell half of them they are prisoners, the other half prison wardens, place them in a makeshift jail and watch what happens.

The Stanford prison experiment was supposed to last two weeks but was ended abruptly just six days later, after a string of mental breakdowns, an outbreak of sadism and a hunger strike.

I remember study this when I did behavioural psychology at uni. A fascinating but totally scary event.

Indeed. It's had very long standing consequences on the way psychological research is done - you'd never be able to run that experiment or anything even vaguely like it today.

Jon