The researchers say police are using resources to combat Internet sex offenses, which are easier to secure convictions, while the majority of men alleged to have directly sexually abused a child are still avoiding prosecution.

Forensic child psychologist Kevin Browne says that only one in 10 men alleged to have committed a sex offense with a child is on the Sex Offenders Register.

"This makes the debate on notifying communities of registered sex offenders meaningless," Browne says in a statement. "But U.K. research shows that only 6 percent of those arrested are linked to the much more severe sexual assaults on children."

Child victims of sexual abuse in England at two in every 10,000, but an survey of young adults' childhood experiences shows the figure to be a lot higher at 11 children in every 100 -- suggesting that most sexual assaults on children go undetected and for every one child identified as a victim of sexual abuse there are 549 child victims who have suffered in silence, Browne says.

Browne's findings are published in the book "Assessing Risk in Sex Offenders" by Leam Craig, Browne and Anthony Beech.