Prosecutors are to receive new guidance on common myths and stereotypes in rape and sexual assault cases, in an attempt to turn the tide on plummeting rape prosecutions in England and Wales.

Revamped advice from the Crown Prosecution Service will cover the use of dating apps and sending explicit photos, as well as the impact of trauma and striking the balance between privacy and a thorough investigation.

Prosecutors are to be told meeting people on hook-up sites and sending explicit photos should not be taken as “blanket consent” for sex, while details about how trauma can impact victims’ memories are to be addressed in greater detail.

The guidance for prosecutors, which comes into effect on 1 November and is subject to a three-month consultation, contains updates on 39 rape myths and stereotypes including false statements such as “If you send sexual images or messages prior to meeting someone, then having sex is inevitable”, and “If you meet men online or through hook-up apps you want sex and should be ready to offer sex”.

Rape convictions in England and Wales have fallen to a record low. Prosecutions and convictions more than halved in the three years to 2019-20 despite an increase in reported rapes. Last year there were 1,439 convictions, although more than 55,000 rapes were recorded by police in England and Wales.

The guidance is an attempt to address conviction rates among 18- to 24-year-olds, which are among the lowest of any age group. In 2018 the Guardian revealed men aged 18-24 were consistently less likely to be found guilty than older men on trial.

The guidance issued also reinstates elements of guidance outlining the “merits-based approach”, which were previously removed. The merits-based approach (MBA) means a prosecutor should treat evidence as if it will be heard by an unprejudiced jury, rather than the “bookmaker’s approach” where a prosecutor tries to second-guess a jury.

Women’s organisations have accused the CPS of quietly moving from a merits-based approach to a bookmaker’s approach, meaning they were less likely to bring a prosecution if they thought a jury could be prejudiced against a victim.

A CPS spokesperson said: “Our approach to prosecuting rape has not changed. Our legal test for prosecution – the full code test – has never included a specific reference to a merits-based assessment because it is already an integral part of the evidential stage.”

Harriet Wistrich, director of the Centre for Women’s Justice said: “We welcome the introduction of new guidance which we hope will improve decision-making by police and prosecutors and begin to reverse the recent dramatic decline in the volume of prosecutions. We believe the decline was largely caused as a result of a retreat by the CPS from a robust approach informed by the ‘merits-based approach’ to decision-making.

“However, the guidance must be properly implemented, we have seen far too many decisions recently infected by the CPS risk-averse approach and a failure to follow existing guidance on rape myths and stereotypes, with the consequence that many victims have been denied justice and perpetrators have been left free to attack again.”

Earlier this year two charities, End Violence Against Women and the Centre for Women’s Justice, were granted a judicial review of how rape cases were being prosecuted by the CPS.

At issue is whether there has been a change in how the CPS prosecutes rape. The Guardian revealed the details of a training roadshow which took place in 2017, where prosecutors were advised that prosecution rates could be improved by taking the “weak cases out of the system”.

Siobhan Blake, rape lead at the CPS, said: “We share the public’s concern about the disparity between the number of rape and serious sexual offences reported and those cases getting to court, and are determined to make significant changes to improve that for survivors of these appalling crimes.

“Clear, up to date guidance is crucial to help our specialist prosecutors make fair and effective decisions and make sure that justice is delivered in every case for victims and alleged perpetrators.”