Sexual predators in the police service must be treated as corrupt officers and rooted out by their senior supervisors, the police watchdog has said.

The Independent Police Complaints Commission said the service was not doing enough to stop suspect sexual behaviour by officers. Instead, it was treating individual cases as isolated, and failing to carry out reviews and learn lessons to prevent such abuse taking place again, the IPCC said in a report published on Thursday.

It warned that failure to stop such behaviour could lead to an escalating scale of sexual abuse against members of the public, or police staff, or both. “This is supported by what is known about how the behaviour of sexual offenders can escalate over time,” the IPCC said.

The report highlights failings that in some cases have allowed individuals with a history of inappropriate behaviour to continue targeting vulnerable women and men they meet while on duty.

Dame Anne Owers, the chair of the IPCC, said more work was needed to identify the scale of the problem. “We do not know precisely how many people have been victims of police officers or staff abusing their powers; we are only aware of the individuals who have had the confidence to come forward,” the report said.

“There is no evidence to suggest it is commonplace. However, the police service does have a responsibility to recognise it as a distinct area of corruption and take steps to reduce its occurrence, identify it as soon as it occurs.”

The report, “The abuse of police powers to perpetrate sexual violence”, comes after a Guardian investigation into the scale of sexual harassment and abuse by officers documented cases of sexual assault, harassment and rape by police officers against women, men and children they met in the line of duty.

The IPCC’s report, a joint study with the Association of Chief Police Officers, began after the jailing in January 2011 of Stephen Mitchell, a Northumbria police officer, for a number of serious sex attacks on women he met through his job. The IPCC was further alarmed by what it says were a spate of cases of abuse and harassment by police officers referred to the watchdog.

Owers said: “The behaviour in this report has parallels with abuses carried out by other professionals such as those in healthcare and social work and the clergy. All are people who are in a privileged position of power – and trust – within society. In the context of the police service, however, this behaviour is also a form of corruption, and it should be dealt with as such.”

The cases examined by the IPCC identified serious failures in whistleblowing systems, with colleagues failing to report suspect behaviour, and in one case failing to report an admission of rape.

“It is essential that a culture of reporting improper behaviour is nurtured and supported by providing staff with an opportunity to voice any concerns they may have confidentially,” the report said.

Other areas of concern include:

• A failure to properly vet officers, particularly those in sensitive posts such as child abuse and domestic violence.

• Lax supervision of officers, especially those who have displayed suspect behaviour in the past.

The report also identified a tendency for the police not to believe vulnerable individuals – most of whom are women – when they reported sexual assaults by police officers. “It is likely that this is the reason they were targeted by the perpetrator in the first place,” the report said.

Owers called on senior officers to “root out this kind of abuse of power” and called for a new code of conduct.

In one case highlighted by the IPCC, a police constable pleaded guilty to one count of misconduct in public office in May this year. He was investigated after a woman said she had been raped by him. The woman, who was known to be vulnerable, made a number of calls to report the attack, but they were not acted on. The officer was suspended and while off work contacted several colleagues admitting that a sexual act had taken place. The report says: “None of the officers reported what they had been told.”