The unprecedented six-month operation, coordinated by the National Crime Agency (NCA) and involving 45 police forces across England, Wales, Scotland and Northern Ireland, exposed the highly organised paedophile network. More than 400 children across the Britain have been safeguarded, the agency said.
Of the 660, 39 people are registered sex offenders but the majority of those arrested had not previously come to law enforcement's attention. Some of those arrested had unsupervised access to children in the course of their work. Doctors, teachers, scout leaders, care workers and police officers are excluded from intensive check to protect children.
The agency estimates that there are 50,000 people in Britain who access child abuse images and videos on the internet.
Sources said that thousands of suspects other than those arrested have been identified by the investigation as it unravels a complex web of online connections. Inquiries are continuing and there will be further arrests, but such is the extent of the offending that police cannot arrest every suspect - the criminal courts would be unable to cope with the caseload and prison overcrowding could hit breaking point.
"This is the first time the UK has had the capability to coordinate a single targeted operation of this nature," NCA Deputy Director General Phil Gormley said.
gOver the past six months we have seen unprecedented levels of cooperation to deliver this result. Our aim was to protect children who were victims of, or might be at risk of, sexual exploitation. A child is victimised not only when they are abused and an image is taken. They are re-victimised every time that image is viewed by someone."
Stating that some of the people who start by accessing indecent images online go on to abuse children directly, Gromley said: "So the operation is not only about catching people who have already offended, it is about influencing potential offenders before they cross that line. We want those offenders to know that the internet is not a safe anonymous space for accessing indecent images, that they leave a digital footprint, and that law enforcement will find it".
According to Simon Bailey, the National Policing Lead for Child Protection and Abuse Investigations, "the vast majority of forces around England and Wales are dealing with an unprecedented increase in the number of reports of sexual abuse of children".
According to John Carr, secretary of the UK Children's Charities' Coalition on Internet Safety, this huge operation "sends out a very clear warning to paedophiles and collectors of indecent images everywhere that the internet is increasingly becoming a very hostile environment for them".
Police forces all over the world are cooperating on an unprecedented scale in pursuit of online child sex offenders and they are deploying technical tools to track them down with ever greater effectiveness," Carr said.