MI5 and its officers will not face contempt proceedings over lies given in evidence to three courts, despite judges proceeding on the basis that there was enough evidence to initiate a case against two senior officers.

The High Court ruled that the investigation required would be unmanageable for the court and that proceedings were not in the public interest. It said police had the necessary powers and resources, leaving open a criminal investigation rather than clearing the officers of wrongdoing.

Baroness Carr, Dame Victoria Sharp and Mr Justice Chamberlain said contempt proceedings were unlikely to do more than duplicate Sir John Goldring’s findings. Misconduct in public office or perverting the course of justice might be more straightforward to prove, with prosecution decisions for the Crown Prosecution Service.

The false evidence concerned Agent X, a violent neo-Nazi informant who coercively controlled his partner, known as Beth, and attacked her with a machete. MI5 helped him go abroad to continue intelligence work while he was under police investigation.

MI5 told three courts it had maintained its policy of neither confirming nor denying his agent status. That allowed information to be withheld from Beth, seriously disadvantaging her legal challenge. In fact, officers had disclosed his status during calls seeking to dissuade a BBC journalist from investigating him in 2020.

The government unsuccessfully tried to block the BBC investigation in 2022 but secured the agent’s anonymity. Beth subsequently sued MI5 at the Investigatory Powers Tribunal and sought a High Court review in 2024.

Goldring’s investigation, ordered by the prime minister, found repeated lying by one senior officer and that another misled colleagues and lied about what he had been told. MI5 accepted its findings without reservation in September. Both officers deny dishonesty; one has resigned and the other faces disciplinary proceedings.

Beth said she was deeply disappointed: “These are extremely serious findings which should demand consequences.” Kate Ellis, joint head of litigation at the Centre for Women’s Justice, called the ruling “surprising”, saying the officers repeatedly refused to admit misleading the courts.

MI5 director general Sir Ken McCallum welcomed the decision but repeated his apology for the failures and the additional distress caused to Beth. The Home Office said the Home Secretary had strengthened oversight, but would not say whether it would refer the matter to police.

The judges warned that Goldring’s findings would inevitably affect courts’ confidence in MI5 evidence. Their ruling leaves unresolved whether MI5 and its director general can legally face contempt proceedings. A criminal investigation remains possible, not confirmed.