Daniel De Simone
Investigations correspondent

This case, which began with violence inflicted by an MI5 agent on his girlfriend, has now become a test of whether courts and the public can believe MI5.

The man, known only as agent X, used his MI5 role to coerce his girlfriend, known by the alias "Beth".

When the BBC sought to name him, the government took it to court and gained him legal anonymity. But MI5 gave false evidence, by saying it hadn't told me he was an agent.

This year the BBC proved the evidence was false, with a recording of an MI5 officer telling me the man was an agent in an attempt to stop me investigating him.

Today, a panel of senior judges heard submissions on the false evidence from the government and the BBC. They were told MI5 now accepts it can no longer maintain its "neither confirm nor deny" secrecy policy on the man's agent status.

By applying their secrecy policy, MI5 had been able to keep much of their evidence secret, including from agent X's former girlfriend.

Speaking after today’s hearing, Beth’s lawyer Kate Ellis says she'll now get a fair trial of her own legal claim against MI5.

"It's a huge outcome for Beth - it's huge - she's had to fight this all the way to the High Court," Ellis says, adding: "I think this case has really undermined MI5's credibility in the courts.”

The court must now decide what to do about the false evidence from MI5. We'll learn their judgement at a later date.

We're at the end of a long day in court, which ended with judges announcing they were going to reserve their judgement on this case for another day. When that will be we don't yet know - but here's what we learnt from the parties involved:

MI5

James Eadie KC - representing the attorney general - started the day with an "unreserved apology on behalf of MI5", after a BBC investigation found the agency had lied to three courts while defending its handling of a neo-Nazi agent.

He also said MI5 recognised that the status of so-called agent X could no longer be protected by the service's usual policy to neither confirm nor deny whether a person is an agent.

"Beth"

Charlotte Kilroy KC, representing X's former girlfriend, said her client agreed with the BBC that the threshold for launching contempt proceedings against MI5 had been met. She argued that "inconsistencies" were "rife" in MI5's handling of the case, and that “copious levels of dishonesty” had not been acknowledged in their investigations.

BBC

Meanwhile, Jude Bunting KC said the BBC was grateful for MI5’s apology - but its position was that the contempt threshold against MI5 had been met. Eadie, representing MI5, told the court more than once that such move would not be "appropriate".

Image source, Julia Quenzler

• If you want to read more about the attorney general's unique role in this case, head to our earlier post

Image source, Julia Quenzler

Thomas Mackintosh
Reporting from the High Court

We're now hearing from Lady Chief Justice Baroness Sue Carr.

"Welcome back to court," she says.

She then adds: "We are going to reserve our judgments."

The hearing concludes and we all rise again.

Thomas Mackintosh
Reporting from the High Court

For the third time today, the court rises as the panel of three judges walk in and re-take their seats.

The barristers, legal teams, journalists and legal observers have all assembled in the slightly less crowded courtroom.

Daniel De Simone
Investigations correspondent, reporting from court

Image source, Avalon / PA

While we wait for proceedings to return to open court - and for our reporters to be allowed back in the room - here's a reminder of the judges presiding over this hearing.

Until today, the MI5 v BBC case has been overseen by one high court judge, Mr Justice Chamberlain.

But he's now joined by the most senior judge in England and Wales, Lady Chief Justice Baroness Sue Carr, and another very senior judge, the President of the King's Bench Division Dame Victoria Sharp.

A panel of three judges, and the identities of the panel, demonstrates how seriously the judiciary is taking this case and the issues that need to be decided - our earlier post runs you through the various options they have.

Thomas Mackintosh
Reporting from the High Court

Eadie wraps up this afternoon’s proceedings by making some final submissions to the panel of judges.

Lasting about 25 minutes, he faces some questions from Lady Chief Justice Baroness Sue Carr and Mr Justice Chamberlain about "motivations".

Eadie concludes by saying - as he did earlier - that the case is "not appropriate for contempt proceedings".

"The suggestion that you can order further witness statements is one thing, but questioning people in advance is very problematic in fairness terms," he tells the court.

That's it for submissions. The court has now gone into a closed session - we'll resume bringing you live updates from the lawyers and judges when they return to open court.

We're hearing more now on MI5's long-standing approach to neither confirm nor deny the identity of agents - a policy known by the initials NCND.

Kilroy tells the court that on Friday 30 May, Beth’s legal team received a note to confirm that MI5 accepted NCND could no longer apply to the man at the centre of this case.

She completes her submissions and sits down.

James Eadie KC, representing the attorney general on behalf of MI5, is now back on his feet.

Thomas Mackintosh
Reporting from the High Court

Bunting asks if he can assist any further and then sits down after finishing his submissions.

Next on her feet is Charlotte Kilroy KC, representing the woman at the centre of this case, known as Beth.

Kilroy briefly addresses the issue of contempt. She says Beth “is not making an application now as her case is still to be heard by the Investigatory Powers Tribunal (IPT).

“We don’t know if more lies were told, we don’t know if more inconsistencies emerged,” Kilroy says, explaining why Beth has decided at this stage not to make an application yet.

“Beth agrees that the BBC’s threshold for contempt has been met,” Kilroy adds.

Kilroy says there are “copious levels of dishonesty” which have not been acknowledged at all in these investigations.

“Inconsistencies are rife,” she adds.

Helena Wilkinson
Reporting from the High Court

We mentioned earlier that judges will consider what, if anything, to do about MI5’s false evidence.

Jude Bunting KC says it is the BBC’s position that the low threshold for contempt proceedings is met.

The barrister says the question for the court is likely to turn on whether the court has had a full and transparent account of what happened.

Referring to the option of initiating contempt proceedings, Lady Chief Justice Baroness Sue Carr asks “against whom”.

Bunting says the threshold is met in respect to Officers 2 and 3, Witness A and MI5.

Helena Wilkinson
Reporting from the High Court

Jude Bunting KC, for the BBC, says MI5 persistently refused to disclose further information.

Bunting says it gives “at the very least the impression of defensiveness”.

The barrister adds that there is “real concern” that the court hasn’t been given a full explanation of what went wrong.

Thomas Mackintosh
Reporting from the High Court

Bunting continues: “We don’t know what happened with Officer 3 as we don’t have a full account from him."

He adds that accounts “lack candour”.

Bunting then notes Mr Justice Chamberlain’s preliminary findings.

“We respectfully echo and endorse those concerns,” Bunting tells the panel of three High Court judges.

• For context: Mr Justice Chamberlain is one of the judges presiding over the case. He has said he has "no confidence" in MI5's account of how a senior officer gave false evidence

Thomas Mackintosh
Reporting from the High Court

All of the members of the MI5 handling team said behaviour by Officer 3 - saying that NCND had been departed from - was “odd” and “weird”.

Bunting adds that the government’s former chief lawyer Sir Jonathan Jones KC, who had been commissioned by Home Secretary Yvette Cooper to carry out the external review, didn't speak to Officer 2 or Officer 3 “at all”.

“Where that leaves us, Person B (also referred to as Officer 2) appears to have consistently lied”, Bunting says, adding that as a result it is “very troubling”.

Thomas Mackintosh
Reporting from the High Court

Bunting references a transcript of a phone call involving a senior agent and the BBC's Daniel De Simone.

“He makes a specific pun which is a reference to one of the groups X is said to have infiltrated,” Bunting says.

He adds that the senior officer was “well aware” of the departure from NCND (neither confirm nor deny).

The decision log we think happened after, in the past tense, that NCND had been departed from, Bunting says.

Quoting another log, Bunting says: “‘I asked X if they would be happy to meet the journalist’ and X said he would, adding he was relaxed about other journalists knowing about his identity.”

Thomas Mackintosh
Reporting from the High Court

Court rises as the panel of three judges walk in and re-take their seats after the lunch break.

Jude Bunting KC, representing the BBC, is continuing with his submissions.

A reminder, there is a ten-minute delay on reporting what we hear in court - but we will be bring you the latest this afternoon as we expect to hear from the lawyer representing the woman at the centre of the case.

Daniel De Simone
Investigations correspondent, reporting from court

While we wait for court to resume, here's how this story was uncovered.

Spies lie, but they are not meant to get caught.

On a wet Friday evening in December, three MI5 lawyers sat in a room at the BBC's headquarters in London.

On the other side of the table were the BBC's lawyers and me. No MI5 officers were present, after we refused a request for the meeting to be secret.

After exchanging strained smiles, we got down to business - and proved to them that the Security Service had been giving false evidence to the courts.

The meeting took place after I told MI5 in November that we were planning to report it had lied and offered it a chance to comment. In response, the Security Service insisted - aggressively so - that it had been entirely honest.

What it hadn't realised until the December meeting, was that I had hard evidence to prove its position was false.

The revelation of the false evidence matters because it raises serious concerns about how reliable MI5's evidence is in the courts, where assessments from the Security Service are given enormous deference.

It also raises fresh doubts about whether MI5 can continue with a core policy of secrecy - after we revealed it was applying it selectively.

Thomas Mackintosh
Reporting from the High Court

While I - and others who've been inside a packed courtroom 72 - find somewhere to eat some lunch, here's a recap of the key lines:

• The hearing started with an "unreserved apology" from MI5 - a barrister said "everyone from the director general downwards acknowledges the seriousness" of the agency giving false evidence over a violent neo-Nazi agent
• James Eadie KC explained that two separate investigations were launched as a result - one externally and another inside MI5. The outcome of the internal investigation is due to be looked at by a senior panel within the spy agency
• Eadie also told the court that MI5's approach to "neither confirm nor deny" (NCND) an agent's identity could no longer be applied to agent X, the man at the centre of this case
• Meanwhile, Jude Bunting KC, representing the BBC, said the corporation was grateful for MI5’s apology - but that an officer who spoke to one of our reporters "did deliberately and repeatedly lie", and there was "widespread knowledge" in MI5 that he had done so

When the hearing resumes, we'll continue to hear submissions from the BBC's lawyer as well as from the woman at the centre of this case.

Thomas Mackintosh
Reporting from the High Court

Eadie has now finished giving his submissions - scroll down to read the submissions he gave on behalf of the attorney general for MI5.

Next to address the panel of judges is Jude Bunting KC - representing the BBC.

He says the BBC is grateful for MI5’s “unreserved apology”.

Bunting then sets out that Officer 2 - mentioned in our earlier post - did in fact "deliberately and repeatedly lie", and says there was "widespread knowledge" in MI5 that he had done so.

"Investigations suggest an absence of candour and do not give a full and tenable explanation," Bunting continues.

Thomas Mackintosh
Reporting from the High Court

As we near the lunch break, James Eadie KC - representing the attorney general for MI5 - lists off three things he'd like the judges to consider in this case:

• He says the court can be "properly satisfied there has been a full and comprehensive investigation", both internally and externally
• Secondly, Eadie says the investigations have covered both individual and corporate responsibility, adding that it has "come to the clear conclusion the errors that had been made had not been deliberate" and that "there had been no misleading or lying"
• The barrister also says there "has been proper accountability for the errors, including in public, in light of the seriousness of the issues"

Helena Wilkinson
Reporting from the High Court

One option for the judges when considering what, if any, action should be taken over MI5’s false evidence is to initiate contempt of court proceedings against the agency itself or individual officers - or both.

Eadie, for the government, addresses that issue in court.

"My submission is that contempt proceedings would not be appropriate", the barrister says.