Rape prosecutions south of the border have fallen to their lowest level since 2008, even though record numbers of allegations have been made to police.

The CPS told the Gazette that it imposed targets on staff between 2016 and 2018 that were “not appropriate” and that may have imposed a “perverse incentive” on prosecutors to shy away from complex cases.

A women’s rights organisation brought a case against the Crown Prosecution Service (CPS) earlier this year, alleging it had made a covert change to its internal practices.

Lawyers involved in the legal action have now said its claim to have made no change in its rape prosecution policy was misleading.

Kate Ellis, a solicitor with the Centre for Women’s Justice, said: “There has been a concerning lack of transparency from the CPS.”

Under its code of practice, the CPS is supposed to charge suspects if prosecution is in the public interest and the likelihood of conviction is greater than 50 per cent. From 2016 onwards, however, the CPS asked staff to bear in mind a second figure – a conviction rate target it called a “level of ambition”. This level was set at 60 per cent for rape. The informal measure was not referred to in CPS reports.

“Levels of ambition are exactly what they sound like – a performance benchmark which the organisation hopes to achieve by the end of the financial year,” the CPS said in a statement. “When setting level of ambition, the intention is that they should be both challenging but realistic to achieve.”

In April last year, the CPS dropped the targets.

“We stopped using conviction levels of ambition as we acknowledged they were not an appropriate tool to measure our success in bringing the right cases to court,” it said.

Criminal solicitor Ian Kelcey, who chairs the Law Society’s Criminal Law Committee, said: “Setting numerical targets is neither an appropriate nor effective tool to deliver justice. It is right that these have been dropped but the CPS should explain how they came about and should adopt a far more transparent approach in future.”