A man has been arrested on suspicion of rape and released on bail, in the case of a woman who claims her own birth is proof her father was a rapist.
"Vicky" alleges her birth mother was a 13-year-old when she was raped by a family friend who was in his 30s.
She believes DNA testing would enable police to formally identify him.
The police force investigating told the BBC's Victoria Derbyshire programme it would now seek the advice of the CPS.
Vicky said it was "positive that things have progressed".
Social services records
Vicky - not her real name - was adopted in the 1970s, at seven months old.
At the age of 18, she began searching for her birth mother and discovered from a social worker and her social services records, that her conception was alleged to be a result of rape.
"It made me feel angry, devastated for my birth mum. For me," she said.
Vicky managed to reunite with her birth mother and, years later, as historical sex abuse cases began to be covered by news outlets in the wake of the Jimmy Savile scandal, decided to act.
Vicky had argued police could use DNA evidence and the social services files that contain the allegations to pursue a prosecution.
But she said she was told by police that she was "not the alleged victim", and so no case could be brought.
"I wanted justice for my mum, I wanted justice for me," she said.
She added that she welcomed the recent arrest, and wants the definition of a victim to be reviewed to potentially include people conceived by rape.
"I'm still determined to get things changed, so that others don't go through what I've been through," she said.