UP to 40 rapists a year are cautioned and allowed to walk free instead of facing jail.
Home Office documents revealed the number of people cautioned for rape has more than doubled in the past decade, while the conviction rate has fallen steeply.
Figures for 1994 show that 19 people were cautioned for rape.
But by 2004 that number had risen to 40, say reports.
Crown Prosecution Service guidelines say a cautioned person must admit the offence and there must be a realistic prospect of conviction.
They adds that indictable offences, such as rape, can only result in a caution in `rare circumstances'.
The Home Office said today that a caution would be used only in exceptional circumstances as a method of dealing with a rape.
These are thought to include old cases of rape, where the culprit was now elderly but the victim wanted to know that he or she had formally admitted the crime.
Another case might include a very young offender who had been referred to action outside the criminal justice system.
A Home Office spokes- man said the Government was committed to bringing more rapists to justice and increasing the poor conviction rate.
Fewer than 6% of rape cases reported to the police result in a conviction.
Although the number of rape convictions has remained stable, the number of rapes reported to the police is increasing.
This means the proportion resulting in a conviction is down from one in three in 1977 to one in 20 in 2004.