Too many police officers and staff have taken sexual advantage of members of the public they were supposed to be helping, a watchdog said.
More than 50 cases over the last two years showed corrupt behaviour by officers which was considered to be sexual exploitation or assault, the Independent Police Complaints Commission (IPCC) said.
It called for more vetting of officers in specific situations, such as those dealing with vulnerable people, and for a code of conduct to set out the behaviour expected of officers.
The report, Abuse of Police Powers to Perpetrate Sexual Violence, found 54 cases of officers or staff trying to form sexual relationships with people they ought to have been helping between April 2009 and March last year in England and Wales.
It went on: "There is no evidence to suggest it is commonplace, but nor can we be confident that all such cases are reported. There are considerable inconsistencies in the referral of corruption cases in general to the IPCC by different police forces. It is therefore possible that the true figure is higher."
Allegations about colleagues were excluded from the figure, as were complaints after a police search in custody. "Nevertheless it is highly likely that there are connections and overlap between these kinds of abuse and further work will be required to explore this," the IPCC added.
The report comes after a rogue officer was jailed for life for raping and sexually assaulting vulnerable women. Stephen Mitchell was ordered to serve two life sentences and warned he might never be freed from prison by a judge at Newcastle Crown Court in January last year.
Trial judge Mr Justice Wilkie said the Northumbria Police constable was a "ruthless sexual predator" who was a danger to women. Mitchell, formerly of Whitley Bay, North Tyneside, preyed on women he met while on duty from his base at Pilgrim Street police station in Newcastle.
The cases studied by the watchdog also included one of a police officer who was accused of rape by a woman with mental health problems who had called for help because she felt suicidal.
The officer initially provided "no comment" answers to questions, but after DNA evidence was recovered he admitted there had been a sexual act, but said it was consensual. He later quit the force.