The official responsible for overseeing the conduct of MI5 has said the security service will now have to provide proof to be believed by judges, after a BBC News investigation exposed how it lied to three courts, the BBC reported.

Lord Leveson, the investigatory powers commissioner and a former Court of Appeal justice, said that as a judge, "if the security service said something to me, then I would accept it." But he said courts would now be "far more reluctant to accept, without evidential proof, things that are said in the future." He praised the impact of the BBC's investigation into an abusive MI5 agent, which he said had led to changes in how informants are managed. He spoke during the first annual conference of the Investigatory Powers Commissioner's Office, or Ipco. The BBC's investigation had "hit the intelligence community hard," including security services around the world, he said.

The investigation exposed how a neo-Nazi informant, known as Agent X, used his state role as a tool of abuse. He coercively controlled his partner, known by the alias Beth, and attacked her with a machete. He had previously abused another woman and threatened to kill her child. Despite this, MI5 protected the agent and helped him go abroad to continue intelligence work while he was under police investigation, even removing his possessions from a police station, the BBC reported.

A secret inquiry, and a warning to the courts

Following the BBC story, a secret inquiry by Ipco concluded the security service knew the agent was a misogynist who was "obsessed" with violence. At the request of the then prime minister, Sir Keir Starmer, Ipco also investigated how MI5 gave false evidence to three courts concerning Agent X. Ipco's report, released earlier this year, found one senior MI5 officer had lied repeatedly while another had misled his own colleagues and lied about what he was told. It also criticised other senior spies and found "serious and systemic failures in MI5's conduct" throughout the case.

MI5 has apologised and said it accepted the report's findings "without reservation." The High Court has declined to launch contempt of court proceedings, and said the police might be better placed to take on the case. In his first interview about the case, Lord Leveson said he stood ready to assist the police if asked. He said that "MI5 have a great distance to go" with courts in the future. He also said the BBC investigation's reach "has been far greater than if this had never happened." Because of the Agent X case, the BBC reported, there is a new policy relating to how agents, also known as covert human intelligence sources, are managed.

The new standard Leveson described is simple and late: if MI5 wants a court to believe something, it should be prepared to prove it. That is not a finding that every past case is tainted. It is a public warning, from the official who oversees the service's conduct, about what judges should demand next time.