Police investigating online child abuse are failing to follow up concerns about suspects, a report has found.

A watchdog investigated forces in England, Wales and Northern Ireland and found one example of officers doing nothing for 18 months despite being aware children could be abused.

The report said officers were dedicated to tracking down abusers, but were being let down by poor training.

The National Police Chiefs’ Council said issues needed to be addressed.

The Majesty’s Inspector of Constabulary examined the work of officers who investigate child abuse images posted online both by paedophiles and children themselves – sometimes as a result of pressure from other children or adults.

The report found forces did not understand the scale of the problem, despite a large increase in cases.

The inspector, Wendy Williams, said online child sexual abuse destroyed lives and forces “cannot afford to wait any longer to improve its response”.

Reports of abuse often come from US-based child protection organisations, the National Crime Agency and tech companies.

Forces then examine and assess images of abuse – including live streams – and add them to a national database, along with a grade for the degree of risk they pose.

The inspector’s report praised the dedication of officers, saying they “often work extremely long hours and on their days off to achieve the best outcome”.

However, it raised concerns that the national child abuse database is not being used to its full potential.

There were long delays in uploading pictures to the database, the report said. Often the same pictures were repeatedly posted online, meaning officers might have to view them unnecessarily. The inspectorate said it was “essential” the database was up-to-date.

In the seven years since police began using digital techniques to identify offenders, thousands of children have been identified as at risk. While this was a “significant achievement”, the report added, follow-up investigations sometimes took months.

“Officers often didn’t consider the risk posed by the suspect to other children”, it concluded, partly because of poor supervision or out-of-date guidance.

“We found that too many investigations were poor. This is partly due to delays in developing intelligence, carrying out risk assessments and taking action. Often these delays are many months long.”

Police forces were not named in the report, but one was found to have more than 100 active cases it had not followed up on in the previous year.

In one example, from September 2020, a suspect had uploaded two videos of a nine-year-old girl being raped by a 17-year-old. The case was “incorrectly” rated as low risk.

There was no further investigation, and when the inspection took place 18 months later, nothing more had been done.

Deputy Child Constable Ian Critchley, from the National Police Chiefs’ Council, said: “We know there is more to do, and we are not shying away from that.”

He said tech companies should be reporting more offenders, a requirement of the Online Safety Bill currently going through parliament. He also demanded better police access to evidence which might be encrypted.

“We are committed to using the findings of this report to support our committed and dedicated staff and partners in how we tackle this national scourge,” he said.