A women’s rights group has launched a legal challenge against the Crown Prosecution Service over its failure to pursue rape cases amid allegations of a covert change in policy on how it handles the crime.

On Tuesday, the End Violence Against Women (EVAW) coalition formally lodged proceedings in the high court against the CPS, alleging that its internal practices have led to a collapse in the number of defendants charged.

Last year, the Guardian reported that a training session at the CPS encouraged prosecutors to take the “weak cases out of the system” to improve its conviction rate. The CPS maintains there has been no change in its approach to prosecuting rape.

The EVAW campaigns manager, Rebecca Hitchens, said: “Every day survivors of rape are being failed by a criminal justice system which appears to have effectively decriminalised rape. We argue that CPS leaders have quietly changed their approach to decision-making in rape cases, switching from building cases based on their ‘merits’ back to second-guessing jury prejudices.

“It is vital that the CPS, a state institution so central to women’s access to justice, is held to account for any internal policy change that has adversely impacted the likelihood of rape cases reaching court.”

The judicial review, where a judge reviews the lawfulness of a decision taken by a public body, will also argue that the actions taken by the CPS discriminate against women and girls and fails to protect their human rights.

A CPS spokesperson said: “There has been no change of policy in how the CPS makes charging decisions in rape cases … We will always seek to prosecute where there is sufficient evidence to do so, in line with the code for crown prosecutors. Decisions to prosecute are based on whether our legal tests are met, and no other reason.”

The move comes as figures from the CPS show rape charges, prosecutions and convictions are at their lowest levels in more than a decade. The number of cases charged by the CPS declined by 38% to 1,758 and convictions fell 26% to 1,925 between 2017-18 and 2018-19.

The CPS has pointed to fewer cases being referred by police and the need to examine more evidence, primarily digital data from complainants’ phones, as some of the reasons for the drop in the number of rape prosecutions.

Harriet Wistrich, the director of the Centre for Women’s Justice, which is bringing the case for EVAW, said: “We have undertaken a major research and evidence gathering exercise and have presented a large mass of compelling evidence from a range of sources, including expert statistical analysis, whistle blowing testimony, a dossier of 20 cases and accounts from police and frontline advocates, which together show that a small cultural shift at the top of the CPS has had a butterfly effect leading to the devastating changes.”