Alison Saunders, Director of Public Prosecutions, said society's concept of rape needed to be challenged, and called for an end to victim-blaming

Date rape suspects will now need to prove that a woman consented as part of tough new rules on the way sex offence cases are investigated.

The Crown Prosecution Service said the time has come to move beyond the idea of 'no means no' when it comes to identifying situations where women may have been unable to give consent.

As part of the major overhaul, the Director of Public Prosecutions, Alison Saunders, said she wanted police to ask suspects how they knew the alleged victim was saying yes, and was doing so 'freely and knowingly'.

The CPS wants to tighten the law against offenders who target people incapacitated through drink or drugs, or where the alleged rapist holds a position of power over the victim.

Questions on consent should also be raised where the complainant has mental health problems or learning difficulties, it was said.

The rules also aims to stop suspects using social media to construct ‘false narratives’ to help cover their tracks.

Numbers of rape cases coming to court in the past two years have risen by 30 per cent but police remain concerned that as many as three quarters of victims do not come forward.

Mrs Saunders said: ‘For too long society has blamed rape victims for confusing the issue of consent – by drinking or dressing provocatively for example.

'But it is not they who are confused, it is society itself and we must challenge that. Consent to sexual activity is not a grey area – in law it is clearly defined and must be given fully and freely.

‘It is not a crime to drink, but it is a crime for a rapist to target someone who is no longer capable of consenting to sex through drink.

‘It is now well established that many rape victims freeze rather than fight as a protective and coping mechanism.’

Speaking at a conference yesterday, Mrs Saunders added: ‘We want police and prosecutors to make sure they ask in every case where consent is the issue – how did the suspect know the complainant was saying yes and doing so freely and knowingly?’

New CPS rules say such situations include where someone is incapacitated through drink or drugs or where ‘a suspect held a position of power over the potential victim – as a teacher, an employer, a doctor or a fellow gang member’.

The ability to consent to sex should also be questioned where the complainant has mental health problems, learning difficulties or was asleep or unconscious at the time of the alleged attack.

Police will be asked to consider whether consent was given freely. Factors which would give the defendant power over the victim, such as being a teacher, doctor or gang member, will be considered

Also covered are domestic violence situations and those where ‘the complainant may be financially or otherwise dependent on their alleged rapist’.

During the conference a hypothetical case was examined by police and prosecutors involving an 18-year-old student in her first week at university who went to a party with an older male student, drank and took drugs then woke to find him in her room.

She repeatedly told him to leave but he took off her clothes and when it was clear that he was about to rape her, she gave him a condom for protection.

Prosecutors and police were asked whether the man should be prosecuted for rape – and an overwhelming number said yes.

On the rise: More than 22,000 rapes were reported to police in 2013/2014 - up almost a third on 2012/13

In discussion of the case, it was recommended that should a complaint have been made, police should check social networking sites as standard practice for evidence and to check if the defendants had posted comments putting a deceptively innocent spin on the night.

New guidelines issued to police and prosecutors warn that ‘offenders may take steps which, on the face might seem normal or reasonable, to distance themselves from an offence or to reframe the offence … in order to undermine or pre-empt any allegation’.

Officers are urged to watch for suspects being over-friendly or seeking reassurance and reinterpreting events leading up to the offence as spontaneous rather than planned.

It is not a crime to drink, but it is a crime for a rapist to target someone who is no longer capable of consenting to sex through drink. Alison Saunders, Director of Public Prosecutions

The conference heard that other examples of behaviour to try to conceal an offence of rape include boasting to friends, pretending to fall asleep afterwards, or making counter-allegations.

Delegates were told by Martin Hewitt, a Metropolitan Police assistant commissioner, that the rise in reporting of rapes was ‘unreservedly welcome’. The conference heard this was partly due to abuse scandals involving figures such as Jimmy Savile and Rolf Harris.

But Mr Hewitt added: ‘The reality is that we are still only getting 20-25 per cent of those who suffer the offence … 75 per cent of those [who are raped] are not coming forward.’

Charities today welcomed the new guidance, saying it could boost victims' confidence in the justice system.

Katie Russell, from Rape Crisis England & Wales, said it was 'vital if the criminal justice system is to become fit for purpose for survivors of sexual violence'.

She said: 'Rape and other sexual offences have long been under-reported, with the Government estimating that only 15 per cent of those who experience these horrific crimes choose to go to the police.

'Through our frontline work at Rape Crisis, we know that among the many reasons for survivors' reluctance to report is fear, including fear of not being well treated by the criminal justice system.

'We hope the police, Crown Prosecution Service and others will continue to strive for positive change of this kind to enable the cultural shift necessary for sexual violence survivors to receive the criminal justice they want and deserve.'