Former UK Prime Minister Tony Blair and his wife Cherie Booth may have been the target of a terror attack, the jury of a trial has heard. The proceedings are being held largely behind closed doors.

The trial, set to be conducted mostly in secret, began at the Old Bailey on Tuesday morning. It is the first case of its kind in UK legal history.

Jury members attending the trial were reportedly told Blair’s address was written on a scrap of paper found in the accused’s car. The paper was allegedly located inside a sunglasses case.

During their search of 26-year-old Erol Incedal's car, police officials made the decision to bug the vehicle according to Sky News.

The prosecution told the jury it was unclear whether the accused had defined a specific target, but suggested he may have intended to target a high-profile British figure or carry out a Mumbai-style terror attack.

Incedal, who is subject to two separate terror charges, was arrested in September last year.

The Crown Prosecution Service (CPS) initially requested the proceedings be held in secret on the grounds of national security, but its application was rejected following an appeal launched by campaign groups and media organizations. Nevertheless, large parts of the trial will be conducted in a covert manner, with journalists bound by unusually restrictive conditions on what they may report.

The accused, originally from London, is charged with two separate offences – engaging in conduct deemed to be in preparation of terrorist activities, and possessing a file entitled “bomb making” on a digital SD memory card. Incedal denies both charges.

The first charge against Incedal, filed under section 5(1) of the Terrorism Act 2006, alleges the accused intended to engage in acts of terrorism or assist other individuals in committing such acts between February 1, 2012 and October 14, 2013.

The second charge relates to the Terrorism Act 2000. Incedal has been accused of possessing a document on or prior to October 13 2013 that was likely to be of use to a person committing acts of terrorism or assisting another in engaging in such acts.

Members of the public and the press are usually granted permission to attend criminal trials in Britain, but in certain circumstances may be asked to leave the courtroom temporarily in the interest of national security.

As the proceedings commenced, the jury of four men and eight women were informed by the judge, Mr Justice Nicol, that certain parts of the trial will remain forever obscured from public knowledge. Nicol said while sections of the trial will be heard in open court, others will be conducted in a more clandestine fashion in the presence of strictly briefed reporters.

The judge added that certain parts of the proceedings, dealing with subjects sensitive to national security, would be held entirely in secret, with both the public and the press excluded.

Incedal's trial is expected to continue for four to six weeks.

Mounir Rarmoul-Bouhadjar, a 26-year-old also from London, formerly pleaded guilty to possessing a document relating to bomb-making. He is due to be sentenced at the close of Incedal’s trial.

Meanwhile, nine separate individuals have been arrested by anti-terrorism police since Monday. Six of the arrests are reported to be linked to the ongoing conflict in Syria.