A woman conceived by rape wants her father brought to justice in a so-called "victimless prosecution", in one of the first cases of its kind, the BBC has learned.
"Vicky" says her mother was under the age of consent when a family friend she claims was in his 30s raped her.
She says her birth is proof of the crime and wants DNA testing to convict her dad of unlawful sexual intercourse.
West Midlands Police says the law does not recognise her as a victim.
Vicky - not her real name - from Birmingham, was adopted in the 1970s at seven months old.
Aged 18, she began searching for her birth mother and discovered from a social worker and her social services records that her conception was a result of rape.
"My birth mum had been 13 - a schoolgirl - and my birth dad was a family friend who was in his 30s," Vicky explains to the BBC's Victoria Derbyshire programme.
"The records said she'd gone to babysit at his house, and he raped her. It says in seven different places in the files that it was rape.
"It states his name and address, that social services, police, health workers knew - but nothing was done about it.
"It made me feel angry, devastated for my birth mum. For me."
Vicky managed to reunite with her birth mother, describing the moment as "very surreal".
Then, years later, as historical sex abuse cases began to be covered by news outlets in the wake of the Jimmy Savile scandal, she decided to act. She had always thought it was wrong that her birth father had not been prosecuted.
"It was then that I thought, 'I've got DNA evidence, because I am DNA evidence. I'm a walking crime scene. And it's all written in the files. Surely people are going to take me seriously'.
"I wanted him to be held accountable. I wanted justice for my mum, I wanted justice for me. The ramifications of what he chose to do have shaped my entire life."
Her birth mother, not wanting to relive the ordeal and having been let down by police originally, decided she did not wish to report the rape again herself - but supported her daughter pursuing it.
Vicky wanted police to consider a so-called "victimless prosecution" for unlawful sexual intercourse with a minor, commonly referred to as statutory rape. She says they could use DNA evidence and birth certificates to prove the ages.
Victimless prosecutions, officially termed evidence-based, can be used in domestic abuse or rape cases, when the victim has withdrawn or declines to give a statement but it is in the public interest to pursue a prosecution, CPS guidance says.
But police, social services, solicitors and MPs have told her she is "not the victim" and so no case can be brought, she says.
A victim is defined by the government as a person who has suffered emotional, physical or mental harm as the direct result of a crime.
"Because of that crime, I am alive. My whole life's been dictated by it, but no-one will see me as a victim.
"I am living, breathing proof of a child rapist and nobody is interested. How is that okay?" she says.
Labour MP for Birmingham Yardley, Jess Phillips, says children conceived through rape should "absolutely" be considered victims.
"The sort of emotional effect that would have on a person, their relationships going forward, on their lives, on how they feel about themselves, it undoubtedly will have affected them.
"I thought we had won this argument, the idea you don't have to be a direct victim of abuse - we would never suggest in a domestic violence situation that a child who had never suffered any violence themselves was not a victim of the crime happening around them - to me it's exactly the same test that is met."
Vicky tracked down her presumed father, wearing a secret camera to record their conversation.
She says he did not deny or confirm having sex with her mother.
"This could be one of the few historical cases where there's actually irrefutable DNA evidence.
"I want the police to demand a DNA test. I want the police and social services to apologise for their failures, and to learn. And I want the definition of victim to be reviewed."
Ms Phillips said the case was definitely in the public interest, as the alleged perpetrator was still alive.
"People who are alleged to have abused over the years, that doesn't just magically go away - these people are a risk to society. Not only do victims deserve justice - regardless of how long ago your abuse was - the authorities should have a prime interest in keeping people safe."
Vicky said: "This has nearly beaten me down. Being adopted comes with so many difficulties, and the trauma of this has affected every part of my life.
"But I will persevere because I know this is so wrong. And I want justice."
Chief Superintendent Pete Henrick, head of West Midlands Police's public protection unit, said the force did not underestimate the psychological affects Vicky had "no doubt suffered".
He said the force had no record of a rape allegation in 1975 and, as such, no record of an investigation, and the alleged victim did not wish to co-operate when Vicky approached them in 2014.
A statement said: "In light of this, she asked whether she could be identified as a victim herself and if the case could be progressed on those grounds. The law does not recognise her as a victim in these circumstances. We liaised with the CPS and were advised they would not support a prosecution.
"Our handling of the case was scrutinised by both our Professional Standards Department and the Independent Police Complaints Commission at the time, and both agreed the police action and conclusion were appropriate."
Birmingham City Council said: "Since April 2018, children's social care services in Birmingham have been provided by Birmingham Children's Trust. Since then we have had no contact with "Vicky".
"We would, of course, be very happy to meet with her if she would find that valuable. It is certainly the case that the way allegations and incidents of harm to children are handled now is very different than was the case in 1975. We would be happy to discuss this with her when we meet."
Update 5 August 2019: This report has been amended following updated information supplied by West Midlands Police.