A secret inquiry by MI5’s watchdog concluded the security service knew an abusive agent it defended in court was a misogynist who was “obsessed” with violence, the BBC can reveal.

The inquiry took place after BBC News originally exposed how MI5 had covered up for the man – a neo-Nazi informant known publicly as agent X.

The government took the BBC to court in 2022 in a failed attempt to block our investigation, but it won agent X legal anonymity.

That year, the BBC first reported how the MI5 spy had used his status to coercively control his girlfriend, including attacking her with a machete, before moving abroad to continue intelligence work while he was still under investigation.

Following the BBC story, the office of the investigatory powers commissioner (IPCO) Sir Brian Leveson launched an inquiry, which – like much of IPCO’s work – was secret. Details of the inquiry can now be reported for the first time.

In response to the new revelations, the spy’s former partner, known as Beth, told the BBC: “I’d like to see a full apology for the fact that MI5 actually were willing to use somebody like X and the fact they were aware of his abuse towards me and they did nothing at all.”

IPCO – which oversees the use of covert investigatory powers, including the UK’s intelligence agencies – concluded:

In a statement to the BBC, IPCO said its inspection “identified serious failings in MI5’s management of agent X” and it “required MI5 to take action to address these failings”.

IPCO added: “MI5 subsequently made significant changes to its policies, practices and procedures, which have been tested at subsequent inspections.

“MI5’s work in this area is ongoing and IPCO will continue to supervise this through its rigorous inspection programme.”

During its inspection, which concluded in 2024, MI5 misled IPCO about having maintained its core “neither confirm nor deny” secrecy policy on X’s status as an agent during conversations with the BBC.

In fact, MI5 had told the BBC he was an agent during early attempts in 2020 to prevent us investigating him.

MI5 also gave false evidence to three courts on this point, leading to a further investigation by IPCO, which is due to report to the prime minister imminently.

In its inspection, IPCO said it found nothing in “case records” to suggest MI5 was aware of any sinister motivation by X for becoming an agent.

The IPCO inspection report was recently disclosed to the BBC in the ongoing legal proceedings, along with other previously secret documents. The proceedings remain live because the court will soon need to consider what action to take about MI5’s false evidence.

One MI5 document, an internal interview with the head of the team that managed agent X, shows him saying X should never have been used as a covert human intelligence source (CHIS), or agent.

“This whole case has been a disaster for everyone, and on reflection, we shouldn’t have touched him [X] as a CHIS,” the MI5 officer said.

For the first time, the government has now publicly accepted the abuse Beth suffered, having spent years trying to undermine her in the courts.

During the original court battle in 2022, the then government tried to cast doubt on the BBC’s case, arguing it rested on “foundations that are anything but solid” and there was “real doubt about the reliability, credibility and motivation of Beth”.

However, in a new statement to the BBC, a government spokesperson said: “The abuse suffered by the woman in this case, known as Beth, was abhorrent and we extend our sincere sympathies to her.”

The statement added: “The use of agents is fundamental to MI5’s ability to keep the UK safe. It is difficult, human work that is governed by legislation and tightly overseen by the Investigatory Powers Commissioner’s Office (IPCO).

“MI5 has procedures to address the risks involved in working with Covert Human Intelligence Sources (CHIS), particularly where there might be individuals at risk of harm, and these have been improved in response to learnings.”

Earlier this year, MI5 paid compensation to Beth to settle a human rights claim she brought against them. It did so without admission of legal liability.

In her first interview since then, Beth told the BBC that she had been “gaslit” by MI5.

“They can’t be trusted because they’ve already lied in court and painted me out to look a certain way and made me feel like I didn’t have a voice or a valid story, but they have now done a 360-degree turn and paid compensation.”

When the organisation paid her compensation, MI5’s director general Sir Ken McCallum apologised for any distress caused by “mistakes in the litigation” but said it related to “record keeping” and stopped short of apologising directly for how she was portrayed.

Beth’s solicitor Kate Ellis, from the Centre for Women’s Justice, said: “The findings of IPCO’s 2024 report are nothing short of devastating for MI5. They show, beyond doubt, that MI5 knew of the warning signs that Agent X posed a serious risk to the public – and to women in particular – but continued deploying him, without managing those risks.”

“We have seen no evidence that the safety of women was even a consideration that MI5 weighed in the balance, when they chose to recruit this man in spite of his history.”

Beth said fighting the case had been “absolutely debilitating at times with the level of trauma and flashbacks it’s caused”.

She added: “I’d like to see a full apology from MI5 for the ways in which they portrayed me.”

Additional reporting by Lorna Acquah