Serial rapists may be escaping justice because of failures by police and prosecutors, a report has shown.
One in eight reported rapes are written off as if no crime ever took place, chances to identify links between offences are being missed, and forces are failing to check the criminal records of foreign nationals, the review found.
The critical inspection report called for police and prosecutors to make changes that "can make a real difference in catching and convicting repeat and serial rapists".
On average, reported rapes were four times as likely as reported incidents of grievous bodily harm with intent (GBH) to end with officers deeming that no crime had been committed, figures showed.
Almost 12% of reported rapes in 2010 were "no crimes", compared with just 3% of GBH cases, the joint report by Her Majesty's Inspectorates of Constabulary and the Crown Prosecution Service (HMCPSI) showed.
"While we acknowledge that no two crime types are the same, we think the comparison is worth making, in order to help illustrate what we believe is a considerable problem," the inspectors said.
The so-called "no crime" figures for rape cases rose to 30% in Kent and fell to 2.4% in Gloucestershire, the review found.
Analysis of a small sample of at least 100 such "no crimes" from each force also showed the decision was wrong in more than one in 10 (11%) cases. Rapists could also be convicted more quickly and successfully if police and prosecutors made better use of available intelligence, the review found.
Profiles used by forces to draw together information on rapes in their area were only up-to-date and in line with national standards in three of the 43 forces in England and Wales. And the potential use of partial DNA samples in eliminating suspects, directing investigations or identifying possible links between cases was also being overlooked, the review said.
Michael Fuller, chief inspector of HMCPSI, added that while progress has been made, "closer working between prosecutors and investigators should be the standard in all rape investigations".