The UK's domestic security service, MI5, has formally accepted that it presented false evidence to three courts during proceedings related to a violent neo-Nazi informant, marking the first time the agency has admitted to lying while defending such an agent.

The admission came during a High Court hearing in London on Friday, where MI5's legal representative, Tim Otty KC, announced the service's acceptance of a critical report's findings. The case centres on a BBC investigation that uncovered the abuse of a woman by the informant, whose agent status was handled by MI5.

MI5 has now acknowledged that it provided evidence based on lies concerning its adherence to a core secrecy policy known as 'neither confirm nor deny' (NCND). The agency had previously claimed to maintain this policy, which allowed it to withhold information from the courts regarding the informant. However, MI5 had in fact disclosed the man's agent status in phone calls to a BBC journalist in 2020 in an attempt to dissuade an investigation.

A panel of three senior judges, including the Lady Chief Justice Baroness Sue Carr, is now deliberating on potential actions, including unprecedented contempt of court proceedings against MI5 or specific officers. The report by Sir John Goldring found that one senior officer, referred to as Officer 2, lied repeatedly, while another, Officer 3, misled colleagues and lied about information received.

Sir John's report also highlighted serious and systemic failures in MI5's conduct throughout the handling of the informant. In response to the report's publication in July, MI5 stated it "fully accepts and acknowledges the gravity of the issues raised" and stressed that "they must never happen again." The service has committed to significant reforms under Director General Sir Ken McCallum.

MI5's legal team argued against contempt proceedings, suggesting they would not be in the public interest given the thorough investigation, the agency's apologies, and its reform efforts. Officer 2 has resigned from MI5, while Officer 3 faces disciplinary proceedings that could lead to dismissal.

Lawyers representing the officers also opposed contempt proceedings. Counsel for Officer 2 stated that the officer accepted his conduct fell below expectations and apologised, but denied acting dishonestly or interfering with justice, and did not accept all of the report's findings. Legal representation for Officer 3 apologised on their behalf, acknowledging that their conduct contributed to the issues.

The case raises significant questions about accountability within intelligence agencies and the potential impact of false evidence on judicial processes. The judges' decision on whether to pursue contempt proceedings will set a significant precedent for how the courts handle such admissions from security services.