Police forces are being ordered to face up to corruption by officers who commit sexual offences against vulnerable women and young people, as figures obtained by the Guardian reveal 169 officers and support staff are under investigation for predatory sexual behaviour.

Senior officers from the 43 forces of England and Wales have held a high-level private meeting to address the problem of officers who abuse their position to make inappropriate sexual advances or carry out sexual assaults on members of the public, many of whom are victims of crime.

The predatory sexual behaviour of officers, ranging from rape to voyeurism, was among the issues at the top of the agenda at the meeting in Chester, and forces have been told the service has to tackle the problem as a matter of urgency, the Guardian has been told.

Figures obtained from 38 of the 43 forces in England and Wales reveal that 169 officers, police community support officers (PCSOs) and support staff are under criminal and disciplinary investigations for sex-related offences.

There are concerns, however, that only 31, or 18%, of the cases are being overseen in any way by the Independent Police Complaints Commission (IPCC).

Debaleena Dasgupta, a lawyer representing women who have been raped or sexually assaulted by police officers, said: "If a woman reports rape or sexual assault by a police officer it is not just that the investigation has to be properly carried out, it has to be seen to be done properly in order for victims to have confidence in the system.

"If these cases are being investigated by the police themselves, then victims are going to get anxious. The IPCC may not have perfect resources but they should be fighting for them in order to investigate these kinds of cases."

The development comes as the former partner of a police officer who was jailed last year for having inappropriate sexual relationships with vulnerable women speaks out against his actions, in testimony seen by the Guardian.

In a film made by Nottinghamshire police, which is being released to all forces next month, the woman said: "I thought he was going to work and doing a professional job, making a difference, and it was all just lies. It affected everybody.

"These people [his victims] were vulnerable. He was in a position of authority. He abused their trust, he abused the public's trust."

The majority of the 169 investigations involve officers or PCSOs and include allegations of rape, sexual assaults, misconduct relating to inappropriate sexual behaviour with victims of crime, voyeurism, accessing indecent images and indecent acts with a child.

Emerging evidence suggests that the victims chosen by police officers were often vulnerable in some way – either women who had gone to the police because they had suffered domestic violence, rape or sexual assault, or individuals who had drug or alcohol addictions.

Five forces did not provide figures, including Leicestershire, which cited exemption Section 30(3) under the Freedom of Information Act, claiming that to give numbers could prejudice inquiries. Northamptonshire police said they were considering withholding the statistics under the same exemption.

A senior source within the police service said: "There are some forces up and down the country who, while they might not be sweeping it under the carpet, are being less than open about what is going on."

Britain's largest force, the Metropolitan police, has set up an internal inquiry to investigate the problem of sexually predatory officers and is taking advice from the Nottinghamshire force, which is acting robustly against such criminality.

The Met's directorate of professional standards is carrying out 42 investigations relating to 47 allegations against officers and PCSOs, including 36 allegations of sexual assault. Sixteen Met officers are awaiting trial for sexual misconduct offences.

In Humberside, where seven officers and staff are under investigation, the IPCC has intervened after a woman complained about the way her allegations of sexual assault by a PCSO in January were dealt with by the force. The PCSO was arrested and questioned, but the case was not referred to the Crown Prosecution Service for criminal charges and the officer resigned a month later, avoiding disciplinary action.

It has since emerged that other alleged victims of the PCSO have come forward and the Humberside force is carrying out a new criminal inquiry, managed by the IPCC.

Detective Superintendent Jackie Alexander, head of the professional standards unit of Nottinghamshire police, where 15 officers and staff are under investigation, said: "We in the police service need to be concerned. This happens in other professions, the church and in teaching, for example, but we in the police have the biggest obligation.

"If people cannot trust the police, who can be trusted? One case is too many for the service and we have got to change our attitude and be alive to the fact that it will happen."

As well as making a film about the problem, her force has introduced a hotline for officers to report concerns.

"We have drawn a line in the sand. We are now finding that more complaints are coming in from colleagues of the officers concerned, or from the officers coming forward themselves, because we are trying to create a culture where this behaviour is totally unacceptable," she said.

Dame Anne Owers, chair of the IPCC, which has urged all forces to do everything in their power to stop such abuse of power by officers, said the police watchdog wanted to get involved in more cases.

"We are currently awaiting the home secretary's proposals on the expansion of the IPCC and welcome the opportunity to extend and strengthen our work. As more resources become available, the IPCC will aim to investigate more abuse of powers cases independently of the police service," she said.

The Guardian first highlighted last year the hidden scandal of the abuse of power for sexual purposes by police officers. Since then, a string of officers have gone through the courts.

Jeffrey Davies, a south Wales officer, faces a jail sentence when he appears at Swansea crown court next week after being convicted of two sexual assaults on victims of domestic violence he met in the course of his duty as an officer. His two senior officers are under investigation for gross misconduct over claims they failed to investigate when the women came forward. Last month Clifford Earl, a Met officer, was jailed for 12 months for groping two women he met in the course of his work.