The spicy courtroom drama has already served up claims of sexually charged scheming, blackmail and computer hacking behind the fortified walls of the secretive city state.

From Monday, lawyers on both sides of a case increasingly seen as a public relations own goal will be able to put some of Pope Francis's closest aides on the stand.

The trial has been adjourned for three months to enable computer experts to recover deleted email, text and WhatsApp messages between some of the accused, one of whom is basing her defence on a claim that she was working on the pope's behalf.

Francesca Chaouqui, a pregnant former PR adviser to the Vatican, is one of five people accused of leaking classified documents that revealed out-of-control spending at the top of the Catholic Church and some top clerics' love of luxury.

She has been granted the right to call as witnesses Vatican number two Cardinal Pietro Parolin and two Francis confidantes, charity supremo Archbishop Konrad Krajewski and Cardinal Santo Abril y Castello, who heads a panel overseeing the scandal-hit Vatican bank.

Chaouqui is accused of conspiring with Spanish priest Lucio Vallejo Balda and his assistant Nicola Maio to leak secret documents they had access to as members of a commission appointed by Francis to spearhead a financial clean-up shortly after his election in 2013.

The two journalists on trial, Gianluigi Nuzzi and Emiliano Fittipaldi, have published books based on the documents at the heart of the trial.

All five accused have been prosecuted under draconian anti-leaks legislation, which could see them receive prison terms of between four and eight years.

The law was rushed onto the Vatican statue book in 2013 as a result of the fallout from the first Vatileaks scandal, which centred on secrets divulged by the butler of now-retired Pope Benedict XVI.

Back behind bars

The Vatican has been criticised by press freedom groups for pursuing the prosecution of the two journalists, who say they were only doing their jobs by revealing problems that believers and the broader public have a right to know about.

With the potential for further embarrassment, some Vatican experts are anticipating a move to bring the trial to a speedy end on procedural grounds.

If the case does proceed to the presentation of detailed evidence, the testimony of Vallejo Balda will be eagerly awaited by the small group of reporters allowed to sit in on proceedings in a rarely used courtroom.

The Spanish priest is reportedly claiming he leaked the documents at Chaouqui's behest because he had become besotted with her after she made sexual advances toward him. She insists he acted alone.

Vallejo Balda spent nearly two months in a police cell last year and, having been released to house arrest just before Christmas, was sent back behind bars days before the resumption of the trial.

Vatican spokesman Federico Lombardi said the monsignor had “breached the conditions of his (house arrest) status by communicating with the outside.”

The books published by Nuzzi and Fittipaldi depict the Vatican bureaucracy that Francis inherited three years ago as being on the verge of implosion thanks to a toxic cocktail of chronic over-spending, feeble accounting systems and serious irregularities in several departments which may have masked corruption.

One of their most striking revelations was that less than 20 percent of donations made by believers around the world under the Peter's Pence scheme ended up being spent on good works.

The rest was swallowed up by the Vatican bureaucracy, partly helping to subsidise the luxurious lifestyles of certain Rome-based cardinals.

The books also highlight irregularities in the system for appointing saints which Francis last week moved to address – proof, the journalists say, that their work is in the Church's interest.