MI5 lied to three courts while defending its handling of a misogynistic neo-Nazi state agent who attacked his girlfriend with a machete, the BBC can reveal.

Arguing for secrecy, the Security Service told judges it had stuck to its policy of not confirming or denying informants’ identities.

In fact, MI5 had disclosed the man’s status in phone calls to me, as it tried to persuade me not to investigate the man – known publicly only as agent X.

The service aggressively maintained its position until I produced evidence proving it was untrue, including a recording of one of the calls.

The BBC can reveal:

• MI5 first lied in a court case where the government attempted to block the BBC from reporting on agent X’s wrongdoing – and succeeded in banning us from naming the foreign national
• The Security Service then repeated the lie to a specialist court, where the woman attacked with a machete – known by the alias Beth – is seeking answers about MI5’s handling of its agent
• It repeated the lie again to a judicial review, where Beth was challenging the specialist court’s decision
• A senior officer said he was legally authorised to tell me X was an agent – so MI5 had not stuck to its policy of not confirming or denying agents’ identities

In an unprecedented admission, MI5 has now issued an “unreserved apology” to the BBC and all three courts, describing what happened as a “serious error” and saying “MI5 takes full responsibility”.

There will now be pressure on MI5 director general Sir Ken McCallum to explain what he knew, given that the officer said he had been legally authorised to disclose X’s role.

It also raises concerns about the reliability of MI5’s evidence in the courts and the sustainability of one of its core secrecy policies.

Beth’s case will now head back to the specialist court, which is investigating if the Security Service breached her human rights by failing to protect her from X’s abusive and coercive behaviour.

It will reconsider whether it was right to rule that the evidence should be heard in closed sessions which she would not be able to attend.

Beth’s lawyer, Kate Ellis from the Centre for Women’s Justice, told the BBC: “I think this raises real concerns about MI5’s transparency, about whether we can trust MI5’s evidence to courts.”

MI5’s lie can be revealed after the BBC applied to the High Court to report false evidence in a corporate witness statement by a deputy director in the Security Service, known as Witness A.

His statement said the service had maintained its long-standing approach to neither confirm nor deny the identity of agents – a policy known by the initials NCND – and gave a false account of the MI5 officer’s calls with me.

During a short hearing granting permission on Wednesday at the Royal Courts of Justice in London, Mr Justice Chamberlain said the relevant MI5 evidence had been “false”.

Home Secretary Yvette Cooper has appointed Sir Jonathan Jones KC, former head of the government legal service, as an “independent external reviewer” to investigate how MI5 came to provide false evidence to the courts.

He has also been asked to recommend any changes needed to ensure that courts are provided with accurate information in future by the Security Service.

After we reported in 2022 how X terrorised his partner, Ms Cooper – then shadow home secretary – had called for an “independent assessment” of the case, looking at the way concerns about “the appalling and dangerous crime of domestic abuse” were handled by MI5.

MI5 says it is conducting an internal investigation into the false evidence which may result in disciplinary action.

Sir James Eadie KC, representing the government at court on Wednesday, said the internal MI5 disciplinary process “indicates the seriousness with which this is being taken”. He said the court will be updated in April.

The BBC has called into question the lack of explanation from MI5. In legal submissions today, the BBC invited the court to take further steps to ensure that this “serious breach is properly investigated” and that the results of any investigation are brought into the public domain.

Exposure of MI5’s false testimony will also damage its credibility in other court proceedings, where judges are obliged to give enormous weight and deference to the Security Service’s evidence.

These often involve secret hearings which are closed even to those most affected – including Beth, people whose relatives have been killed in attacks and people whose UK citizenship has been stripped from them.

MI5 has acknowledged the issue, saying in legal submissions on Wednesday that it is “acutely conscious of the particular responsibilities that MI5 bears” and that courts must be able to “trust completely any evidence it provides”.

The Security Service maintains that the NCND policy is essential to maintain national security and keep agents safe. But the BBC revelations will add to concerns about the way the policy is being used, including that it may stand in the way of agents being held accountable when they abuse their positions or commit crimes.

Because the senior MI5 officer told me disclosure of the agent’s status had been legally authorised, it means it had been signed off by lawyers and other senior figures in MI5. The Home Office and Cabinet Office should also have been informed, according to the policy for departures from NCND.

After Wednesday’s hearing, a government spokesperson said: “Ministers and civil servants are not routinely consulted on private disclosures by the agencies and were not on this occasion.”

In a new witness statement, the MI5 deputy director Witness A said he “sincerely” apologised for giving incorrect evidence.

He said the false information “reflected my honestly held belief at that time, and which accurately reflected the information I was given”.

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