When Ruth walked into a police station to allege she had been raped by her partner, she did not think that she would end up in the dock.

She would later be accused by police of making a false rape allegation, charged and put on trial. It led to a years-long struggle to clear her name, before she was eventually acquitted.

Ruth, whose name we have changed to protect her identity, reported the alleged rape in early 2020 – seven months after she and the man, a police officer, had split up. The day of the alleged assault was the last time the pair had seen each other.

“I felt if I didn’t report it, I couldn’t carry on with my life anymore,” Ruth tells File on 4 Investigates.

While the accused man was not charged with a crime, Ruth faced an accusation of perverting the course of justice, an offence that carries a maximum life jail term.

In the UK, only an “extremely small number” of people every year are prosecuted for making false rape claims, according to the Crown Prosecution Service (CPS).

The latest official CPS figures, from more than a decade ago, show there were 5,651 prosecutions for rape in England and Wales over a 17-month period in 2011-12 – compared with 35 prosecutions for making false allegations of rape. Around the same time, CPS guidelines were updated, leading to a drop in false rape prosecutions.

Someone falsely accused of rape before a trial is likely to spend time in a police cell or even prison. If they are charged, their name will normally be made public. Even those quickly exonerated can face stigma.

Current CPS guidance says it is important that police acknowledge the damaging impact a false rape allegation can have, and that these cases should be dealt with robustly.

“The bar for these prosecutions is rightly high,” it told us, and “charging decisions must be approved by lawyers at the highest level of the organisation”.

In Ruth’s case, the judge said it seemed as though “the whole prosecution was launched on a false basis”. He raised serious questions about the handling of the case – including one key piece of evidence: a secret audio recording made by Ruth’s former partner.

This report contains explicit and distressing references to alleged sexual assault

Ruth’s relationship with the man she accused was brief but intense.

It came to an end in summer 2019, after a painful sexual encounter that she alleged to be a rape.

Ruth had reluctantly agreed to a particular sex act, but says she had made two conditions – one of which was that her partner should stop if she told him it hurt.

She says she then explicitly withdrew consent during sex.

“It was really, really, really painful,” she says.

However, she says her partner did not stop.

Afterwards, the pair argued, and Ruth’s partner told her the relationship was over.

Ruth says she had been left in so much pain that she went to her GP, who sent her to hospital for swabs and an examination. She had been raped, she believed.

“I wasn’t gonna report it because he was a police officer,” she says.

She tried to forget about what happened but, when struggling with intimacy in a new relationship months later, decided to make an allegation of rape to Warwickshire Police.

Ruth’s ex-partner – an officer with neighbouring West Midlands Police – was arrested and questioned, but denied he had raped her.

As evidence the sex had been consensual, he produced an audio file he had secretly recorded on his mobile phone during the sex, which he said proved Ruth was lying.

It would later emerge in evidence that investigating Warwickshire officers had agreed with him that they could hear her “laughing and consenting”.

Six weeks later, Warwickshire Police said no further action would be taken against Ruth’s ex-partner.

She, however, then received a phone call from the force asking her to attend a voluntary interview.

“I thought they really truly honestly were supporting me and then it very quickly turned,” she says. “They said I was a scorned woman, he didn’t want me, so therefore I cried rape.”

It was in her police interview that Ruth found out about her ex-partner’s secret audio recording.

In November 2020, nine months after making her allegation, Ruth was charged with perverting the course of justice.

Perverting the course of justice means deliberately interfering with the justice system. It covers crimes such as giving a false alibi to protect a friend or relative, destroying or hiding evidence, threatening witnesses or making a false allegation.

When prosecuting suspected false claims of rape, police forces in England and Wales must escalate any decision to charge to the highest level, by notifying the director of public prosecutions.

According to CPS guidance, authorities must have evidence to prove someone has made a false allegation.

In Ruth’s case, as well as the audio recording, investigating officers said there were significant inconsistencies between the allegations Ruth had made and earlier WhatsApp messages she had sent her then-partner, giving consent to having sex.

When Ruth’s trial finally began, in April 2023, prosecution lawyers told the court that the recording and messages, plus her behaviour before and after the encounter, were proof she had been lying.

They referred to a transcript of the recording, but chose not to play the audio to the jury.

However, Ruth’s barrister, Sophie Murray, did.

As the recording played, Ruth could be heard saying she was in pain and telling her partner “no” and “get it out”.

The sounds of laughter and enjoyment did not come from Ruth.

Her defence team had analysed the audio file and found they had in fact been made by actors in a porn film that was playing in the background.

“All of a sudden the whole room changed,” Ruth recalls.

It was the first time she had heard the recording of the alleged rape. She describes it as “worse than I remember”.

Murray recalls listening in court to the audio of Ruth, who was sitting behind her in the dock, clearly in pain. It was “probably one of the hardest moments of my professional career”, she says.

Ruth’s defence hinged on the idea of her “conditional consent” having been breached. The Sexual Offences Act 2003 states a person can lay down conditions when consenting to sex – for instance, that a condom is worn. If those conditions are violated, the sex is considered non-consensual.

In his victim impact statement, Ruth’s ex-partner described having been accused of rape as a “living nightmare” and said Ruth had categorically agreed to the sexual encounter.

However, under cross-examination by Murray, he admitted Ruth had asked him to stop the sex act if it hurt – and that he hadn’t.

The man is currently suspended from West Midlands Police on full pay. He faces a misconduct hearing later this year into whether making the audio recording of the sexual act without her knowledge breached the police code of ethics.

We tried to contact him, but he did not respond.

• A list of organisations in the UK offering support and information with some of the issues in this story is available at BBC Action Line

The jury took just over an hour to find Ruth not guilty of perverting the course of justice.

As it had not been a rape trial, the verdict did not mean the jury found that she had been raped – only that she believed she had been when she made her allegation.

“I didn’t cry, I didn’t scream,” she says of being found not guilty. “I don’t really know what I felt if I’m honest.”

The judge raised questions about how the CPS and Warwickshire Police had made their decisions. He also asked for the original rape investigation to be reopened.

The CPS told the BBC it takes every allegation of rape extremely seriously, and that in exceptional cases, and in Ruth’s case, the evidence was reviewed by multiple senior specialist prosecutors. However, it added, it respects the jury’s decision.

In a statement, Warwickshire Police said the original decision to charge Ruth with perverting the course of justice had been taken in consultation with the CPS.

After her trial, it added, “a thorough review was conducted of this case and the original rape investigation, by independent officers who had no prior involvement in either case”.

Advice was also sought, it said, from a different CPS area to ensure an independent perspective – but it was “again established that there was still not enough evidence to be able to pursue a rape charge and the decision was to close the case”.

The victim was kept updated throughout the review process, said the force, and that it takes “all reports of rape extremely seriously and does everything it can to support victims of rape” and has also “invested more resources into rape allegations”.

The fact the suspect in the rape investigation is a serving police officer did not impact the investigation and meant there were additional levels of scrutiny, added the statement.

The force that employs Ruth’s ex-partner, West Midlands Police, told us that an investigation into matters of conduct was carried out after Ruth’s trial, as internal investigations are not progressed during criminal proceedings.

It said that while the investigation into the officer happened as quickly as possible, it had to take place “within a strict legal framework, meaning serious or complex cases can take time”.

Ruth says she feels let down by the decision not to prosecute her ex-partner, but that she does not regret reporting the alleged rape.

“I can honestly say everything I’ve done is right for myself and for other people,” she says. “Hopefully no-one will be in the same position as me.”