Rape and sex assault victims are being let down in as many as one in three cases, a study by the prosecution watchdog suggests.
Inspectors found specialist CPS units had insufficient resources and staff and warned the level of care provided to complainants is "falling well short of what is expected".
A review of 85 applicable cases by HM Crown Prosecution Service Inspectorate (HMCPSI) found that 53 - less than two in three - were dealt with by a rape specialist.
Victims also faced staffing changes, with "continuity of prosecutor" in just 44 of 72 relevant cases.
Of a total of 90 files examined, it appeared that they were dealt with in a dedicated unit in only 42 cases, with a further eight where the situation was unknown.
There was compliance with all relevant victim policies in 66.7% of cases.
HMCPSI said that since Rape and Serious Sexual Offences (Rasso) Units were rolled out in CPS areas in England and Wales in 2013, different models have developed in each area - leading to a lack of consistency and limited compliance with minimum standards.
Chief Inspector Kevin McGinty said: "While I acknowledge that considerable work has been undertaken by the CPS to prioritise improvement in rape prosecution outcomes, and that work continues, our inspection showed that the level of care being provided to victims in these sorts of cases is currently falling well short of what is expected.
"It is essential that the CPS makes sure that the minimum standards required for these units are met more consistently to ensure they provide a better service to victims and witnesses in these sensitive cases.
"The level of performance must improve."
Feedback from police, counsel and the judiciary suggested that because workloads exceed units' capacity, it is difficult to achieve "quality casework", the report said.
It went on: "In addition, it was felt that there is considerable pressure on the CPS to improve on success rates and to prosecute more cases, which may lead to some cases being pursued even though there is little chance of obtaining a conviction after a trial.
"Further, that decisions on cases are rushed to achieve timeliness targets and then subsequently dropped when more thought is given to the detail of the case."
HMCPSI made a number of recommendations for improvement, including that CPS Headquarters provides detailed guidance of the recommended national model to be deployed locally and that all Rasso lawyers undergo refresher training.
The report acknowledged that the service was undertaking its own internal review of its Rasso units, which did not fall within the inspection timeframe.
Director of Public Prosecutions Alison Saunders said:"The CPS has already made considerable progress since this inspection was carried out," she said.
"Most of the recommendations within this report had already been identified by the CPS and were being addressed before the report was published.
"However, there is always more that we can do.
"The CPS has taken a leading role in the criminal justice system's response to rape, reversing a fall in the volume of rape referrals identified in 2012/13."
She said dedicated teams now handle all specialist rape and sexual offence cases, adding: "The CPS saw the highest ever numbers of these cases last year, with the highest ever volumes of charges, prosecutions and convictions."