As one of the detectives told me: 'You've got to get their mobile phones examined, their computers examined, their cameras examined and look at every single image.Multiply that by the number of prisoners and it's a phenomenal amount of work.' It's a meticulous and timeconsuming approach, but it works.In fact, she was John Taylor, a middle-aged detective and a Covert Internet Investigator (CII) with the Paedophile Unit.To catch the new breed of paedophile, you see, has required a new form of policing and Scotland Yard's Paedophile Unit has led the world with its pro-active approach.But despite often having no criminal record, they pose every bit as serious a threat to our children as the more readily identifiable 'dirty old men' of the past.'In the past couple of years we've arrested magistrates, lawyers, company directors, police officers, people in the media,' DCI Stevens tells me.
But he's not booking cinema tickets or tracing his family tree or doing any of the things that have made the internet such a valuable tool of modern life.
What my time at the Paedophile Unit has revealed is that the days when a lazy stereotype of a paedophile - a male, middle-aged loner, often still living with his parents - are long over.
Yes, child protection officers do still come across the sad and dangerous individuals who could be described in that way, but increasingly they are arresting a new breed of paedophile.
It's very real, it's very nasty indeed and the connection between those internet chats and images of paedophilia are all too common.
I've spent the past 18 months shadowing the officers of Scotland Yard's Paedophile Unit and, despite being a former detective with more than 12 years of experience in child protection, I've been horrified by what I've seen.