A BBC broadcast would damage national security and create “a real and immediate risk of serious or life-threatening harm” to an alleged MI5 agent if it identified him, the High Court has heard.

The broadcaster wants to air a report which would identify a “dangerous extremist and misogynist” who is allegedly an MI5 agent, and argues it is in the public interest for his identity to be revealed.

The proposed report would claim the man, identified in proceedings as “X”, used his status as an agent to abuse, control and coerce a former partner, referred to by the pseudonym “Beth”, and that MI5 either knew or ought to have known about this and it was wrong to use him as an agent.

Attorney General Suella Braverman is seeking an injunction to block the broadcast, arguing that there is no public interest in identifying him which would override the risk to the man’s life and the impact on national security.

Mr Justice Chamberlain is considering the case at a two-day hearing at the Royal Courts of Justice in London which started on Tuesday.

Lawyers representing Ms Braverman said that she “neither confirms or denies” the BBC’s claim that X is an agent, or covert human intelligence source (Chis), but is conducting the hearing on the “hypothetical assumption” that he is or was.

In written arguments before the court, Sir James Eadie QC, for the Attorney General, said: “Publication of the report would constitute a breach of confidence/false confidence by the BBC.

“To do so would damage national security and the public interest. It would also create a real and immediate risk of serious or life-threatening harm to X.

“Those impacts establish the most powerful public interests in restraining publication.

“There is no public interest in publication that could be said to override such interests.”

The case of wrongdoing by X, and the subsequent speculation that MI5 must have been aware of it and failed to react appropriately, rests on foundations that are anything but solid.

The barrister said that there are “avenues for complaint and investigation” in relation to any allegations against MI5, which have been set up “precisely to avoid the sort of damage to the public interest that the BBC’s proposed report would produce”.

He argued that identifying X as an MI5 agent was “obviously confidential” information.

Sir James also said the “most serious” allegations against X have been investigated by police and no further action was “considered appropriate to be taken”.

He added: “The case of wrongdoing by X, and the subsequent speculation that MI5 must have been aware of it and failed to react appropriately, rests on foundations that are anything but solid.

“There is real doubt about the reliability, credibility and motivation of Beth. Police and the Crown Prosecution Service (CPS) have been involved but the outcome has been no action – in significant part because of those doubts.”

The Attorney General says there is no objection with a broadcast about the allegations against X and MI5’s use of agents which does not identify him, but argues that identifying him would be a breach of confidence and infringe X’s human rights.

However, Sir James said the BBC has “no interest in producing an anonymous or diluted” version of the report.

The BBC says that the broadcast of the story, and the identification of X by name, is in the public interest and is contesting the application for an injunction.

Mr Justice Chamberlain gave some details of the case in a ruling last week.

He said the proposed programme includes “allegations that X is a dangerous extremist and misogynist who physically and psychologically abused two former female partners”.

It also includes allegations that X is a Chis or agent for the security service, that he told one of the women that he worked for MI5 “in order to terrorise and control her”, and that MI5 “should have known about X’s behaviour and realised that it was inappropriate to use him as a Chis”, the judge said.

There will be a closed procedure, for which special advocates – security-cleared lawyers – will represent the BBC’s interests, and an open part of the proceedings, some of which can be attended by the press and public.

Mr Justice Chamberlain made an order at the outset of the hearing on Tuesday that reporting of the open hearing should be delayed to ensure that nothing is inadvertently revealed in public which should not be.

When the judge gives his ruling on the injunction, there will be both an open judgment which will be made public, and a closed judgment which will be seen only by the Attorney General’s legal team and the special advocates.