Cachella Smith
Reporting from the High Court

The start of these proceedings tracks back to a man, known publicly as X, who served as an informant for MI5.

A BBC investigation published in 2022 found X had used his position as a means to terrorise his partner, known as Beth. Video evidence showed him threatening to kill her and attacking her with a machete.

The government had sought to block publication of this – failing to do so completely although succeeding in preventing publication of the man’s identity, which is why we call him X.

During these proceedings, and those brought by Beth, MI5 told three separate courts that it had stuck to its core secrecy policy of neither confirming nor denying X was a state agent.

However, the BBC in February produced notes and phone call recordings proving MI5 had disclosed the man’s status to them during attempts to prevent its investigation into the matter. It meant the agency had given false evidence in court.

The agency has since issued an "unreserved apology" – calling what happened a "serious error".

And that brings us to where we are now, and a situation that has raised questions about the reliability of MI5's evidence to courts generally as well as their policy of neither confirming nor denying the identity of who works for them.

Daniel De Simone
Investigations correspondent, reporting from court

Three High Court judges will rule at 14:00 BST on what to do about false evidence given by MI5 to three courts.

MI5 stands accused of deliberately lying when trying to block the BBC from publishing a story about a neo-Nazi state agent, who abused his partner.

MI5 claimed it had never breached its core secrecy policy of neither confirming nor denying that the man was an agent, but the BBC proved it had. The case has become a major test of how the courts see MI5 and the credibility of its evidence.

The Lady Chief Justice Baroness Sue Carr, and two other senior judges, will decide if MI5’s explanations for the false evidence are adequate or whether the court needs to take further action.

I'll be in court with my colleague Cachella Smith to bring you the latest.