Almost one in every 35 men could pose a sexual risk to children, new figures suggest.
The research by the National Crime Agency - which recently became operational in Northern Ireland - found that as many as 3% of men could be a potential sex abuser or have an interest in online child porn.
The NCA's deputy director Phil Gormley said that of those, as many as 250,000 men were "true paedophiles" -attracted to pre-pubescent girls under 12.
He said a new approach was needed to protect children, saying: "If all we have is arrest and incarceration, that will not help them come forward. Like most people I am shocked by the estimated number who have this interest. It tells us some unhealthy things about human nature."
The issue of child sex abuse has been thrust into the spotlight in recent months and years through high-profile scandals including DJ Jimmy Savile's sex abuse on an epic scale and the grooming gang scandals in Rotherham and Oxford.
Last week a new report by the NSPCC found that the number of children at risk of all forms of abuse in the UK had increased by 80% since 2002. The NCA figures, based on academic and other sources, suggested that between 1% and 3% of men had paedophile tendencies, with Mr Gormley saying: "Whatever the exact figure, it is big."
Writing in the Mail on Sunday, Karen Bradley, who was appointed as the first minister for preventing abuse and exploitation, said society was at a "watershed moment" and needed to look at the reality of what was going on.