London — As reports of rape made to police in England and Wales have increased exponentially, rape charges, prosecutions, and convictions have all fallen to their lowest levels since record keeping began, according to government statistics. Women's groups allege this is due, in part, to a shift in prosecutorial policy, and they are seeking to take government prosecutors to court over it.

CBS News reviewed data from Britain's Crown Prosecution Service's (CPS) annual Violence Against Women and Girls reports, as well as from its Office of National Statistics, which show that, since 2007, there has been a 363% rise in rape allegations made to the police in England and Wales. In the same period, the number of rape charges against suspects has fallen by 15.5%.

Britain's Crown Prosecution Service Inspectorate (HMCPSI) — an official government watchdog — said in a report released late last year that the wide gap in the statistics "is a matter of serious concern," and is due to a criminal justice system that is "close to breaking point."

A graph shows the number of reports received by police in England and Wales of alleged rapes over about 10 years, in blue, compared to the number of rape charges filed against suspects during the same period, in red, according to official data.

The watchdog group's report was part of a wide-ranging and ongoing government inquiry into how rape cases are handled across the criminal justice system in England and Wales, the rest of which is expected to be released this summer. It blamed a lack of resources at the Crown Prosecution Service (CPS) and problems with processing digital evidence, among other things, for the startling numbers.

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But the U.K.'s Centre for Women's Justice (CWJ) and the End Violence Against Women Coalition (EVAW) allege the severe drop in charging and prosecution rates over the last two years is due to a covert, discriminatory and illegal shift in prosecutorial protocol, and they have requested a judicial review into the CPS.

"National emergency"

"I was told by the police that I had a really strong case – my rapist was known to them, and unknown to me ,he had a history of violence against previous partners, plus I had evidence of the attack," Rebecca, whose name has been changed to protect her identity, said according to a statement put out by EVAW announcing its request for a judicial review.

Rebecca said she was held prisoner for two days by her then-boyfriend, during which time she was raped at knifepoint. After the attack, she continued speaking with him, both in person and via text message. When police were called by a friend to her residence, she turned them away. She was later told by authorities that, because of her behavior, her case would not be taken to trial.

"A judgment was made about my physical reaction to being raped not being the right one, and the CPS dropped my case. I was denied my day in court and this man was able to walk free and not answer for what he did to me," she said.

"If another kind of crime that serious was so unlikely to be prosecuted and punished, there would be a national uproar and it would be a national emergency," Katie Russell, National Spokesperson for Rape Crisis England & Wales, told CBS News. "So why not for this? Why is it not being treated as the priority it should be?"

Decision to prosecute

For almost a decade in England and Wales, prosecutors were instructed to take a "merits-based" approach in deciding whether to pursue a rape case. That meant lawyers were told to consider the laws on rape — including whether consent was given and whether the victim was in a state where they could give consent at the time — rather than what a real world jury, made up of people who could be influenced by stereotypes about rape, might think.

The reason for this "merits-based" approach was to prevent prosecutors from rejecting cases which, while they might have the law on their side, could fail to convince members of a jury.

Over the last three years, the merits-based approach has been largely erased from CPS guidelines for prosecuting rape cases, according to EVAW. Now those guidelines require that prosecutors believe there to be a "realistic prospect of conviction" before moving forward with a case. In that same timeframe, reports of rape have continued to increase, but prosecutions have fallen to their lowest levels since current record keeping began.

"It's our position that the unlawful removal of this approach meant that CPS prosecutors took a more risk-averse attitude towards prosecuting rape and were charging only the strong cases and not charging the so-called weaker ones," Rebecca Hitchens, campaign manager at EVAW, told CBS News.

"What's being taught or told to perpetrators of sexual violence is: You can get away with it."

The Crown Prosecution Service denies that there has been a change in protocol, and says it removed the "merits-based" approached from its guidelines because it was causing confusion.

"Every decision is, and always has been, taken in the same way, following the Code for Crown Prosecutors. No individual charging decision is influenced by any factor other than the merits of the case," a CPS spokesperson told CBS News.

"The growing gap between the number of rapes recorded, and the number of cases going to court is a cause of concern for all of us. We will implement any improvements suggested as part of the ongoing, cross-justice system rape review," the spokesperson said.

Maddie Richards contributed to this report.