The police chief in charge of child protection says tens of thousands of British men have shown an interest in sexually abusing children.

Simon Bailey said investigators monitoring a single online chatroom in 2017 identified 4,000 men using it from the UK alone.

Bailey, the National Police Chiefs’ Council lead on child protection, estimated the number of men interested in sexually abusing children at more than 20,000. He said the figure was comparable to the number of current and former terrorism suspects.

He added that limited resources meant not all perpetrators could be tackled, with police forced to focus on the most dangerous offenders. “We are having to prioritise the threat,” he said. “Some lower-level offenders cannot be arrested and taken to court. There is just not the capacity.”

Bailey warned that a growing threat to children came from live streaming and said police wanted a fresh crackdown from tech companies on the use of platforms including Periscope, which is owned by Twitter, and Facebook Live.

His warning follows recent reports that abusive behaviour is on the rise. Earlier this month, the NSPCC child protection charity said there had been a 31% increase in the number of reported cases of child sexual abuse in the UK in the previous year.

Bailey said reports to child protection experts were up 700% since October 2013, although some put that increase down to a greater willingness to report offences.

In the first 11 months of 2017, the National Crime Agency received 72,000 referrals about online child sexual abuse imagery, up from 6,000 in 2010.

Bailey, who is the chief constable of Norfolk, said he was in no doubt that the dangers had grown, even if awareness had too. “I think there is more sexual abuse of children being perpetrated both physically and virtually,” he said. “There are more men than five to 10 years ago who are trying to abuse children.”

And he emphasised that online abuse was not without consequences. “If a child flashes their breasts to someone online it can still cause great damage [to that child].

“I believe there are tens of thousands of men that are now going into chatrooms and forums with a view to grooming children,” he added. “Technology has afforded an access to children that people who have a sexual interest in children never had before.”

Bailey said police did not have enough officers to successfully pursue all child sex abusers and even thousands more detectives would not bring every offender to justice, even though the law was sufficiently robust to allow for prosecutions in most cases. “There are hundreds of officers tackling this now,” he said. “Thousands and thousands still would not be enough.

“This is one of those wicked problems we simply cannot arrest our way out of.”

The police chief said the children being targeted were not just those from homes where the parents or the adults in charge were neglectful. “The victims have included children of very capable and very caring parents. It does not recognise social status. The victims include children of middle-class, educated parents who think they are internet-savvy,” he said.

About half of parents warned their children about the dangers of the internet, Bailey said, but it needed to be a frequent and repeated warning. “That is usually a one-off conversation – it needs to be constantly reinforced,” he said. “At Christmas parents buy children internet-enabled technology. They need to understand the risks.”

Schools have recently started telling children about what to do if they are caught up in a terrorist attack. Bailey said education on the dangers of child sexual abuse also needed to be taken into the classroom. “We need the same warnings about sexual abuse in schools, in the same way as we do for terrorism.

“Young people need to be educated about the risks, and spot the signs of exploitation and have the confidence to report it.”

Some 20% of new imagery is self-generated and is often taken by other children. But Bailey said he did not regard those who viewed sexual images of children under the age of 16 as harmless under any circumstances.

“There are more men viewing imagery and asking kids to flash,” he said. “Viewing an image is abusing a child.”

He added that most offenders across all categories of child sexual abuse were white, despite the considerable attention that has been paid in some parts of the media to so-called Asian street-grooming gangs.

On the emerging issue of live streaming, Bailey urged tech companies to do more. “Software providers have a critical role in policing the environment they create,” he said. “They have a social and moral responsibility to make their platforms safe for children to use.”

The Home Office said: “We are supporting a robust law enforcement response, developing new capabilities to identify and protect victims and working with the internet industry to remove illegal images and tackle grooming.

“This is a global problem that demands a coordinated global response. Internet companies have made progress but they must work harder to remove and stop online child sexual exploitation.”