The Great Reformer, by the British Catholic writer Austen Ivereigh, nicknames the group “Team Bergoglio” and says members toured private dinners and other gatherings of cardinals in the days before the conclave, quietly putting their case.

Cardinal Bergoglio was effectively the runner-up in the 2005 conclave, in which Joseph Ratzinger was elected, having been put forward by an alliance of mainly European reformists.

But it later emerged that his chances of election were hampered by what amounted to a dirty tricks campaign by opponents from Argentina.

He also effectively pulled the plug on any campaign in 2005, urging would-be supporters to throw their weight behind Cardinal Joseph Ratzinger and making clear that he did not wish to be the focus of a faction.

By 2013, he had been largely discounted by most commentators, partly due to his age, as well as because he had signalled that he did not wish to stand in Cardinal Ratzinger’s way.

But by last year, the appetite for reform in the Vatican and a pope without links to the establishment, widely seen as corrupt and riddled with in-fighting, had become intense.

“Spotting their moment, the initiative was now seized by the European reformers who in 2005 had pushed for Bergoglio,” Mr Ivereigh, who once served as Cardinal Murphy-O’Connor’s press secretary, explains in the book.

He wrote that Cardinal Murphy-O’Connor, then 80 and no longer with a vote in the conclave, teamed up with the German cardinal Walter Kasper, whose controversial call for remarried divorcees to be allowed to receive communion was one of the main points of division at the synod that Pope Francis held in Rome this year.

Cardinal Murphy-O’Connor’s role included lobbying his North American counterparts as well as acting as a link for those from Commonwealth countries.

“They had learnt their lessons from 2005,” Mr Ivereigh explains. “They first secured Bergoglio’s assent. Asked if he was willing, he said that he believed that at this time of crisis for the Church no cardinal could refuse if asked.

“Murphy-O’Connor knowingly warned him to 'be careful’, and that it was his turn now, and was told 'capisco’ – 'I understand’.

“Then they got to work, touring the cardinals’ dinners to promote their man, arguing that his age – 76 – should no longer be considered an obstacle, given that popes could resign. Having understood from 2005 the dynamics of a conclave, they knew that votes travelled to those who made a strong showing out of the gate.”

A key turning point came during the series of closed meetings before the conclave, known as congregations, when Cardinal Bergoglio gave a short but moving speech about the state of the Church.

But, the book argues, a ban on official updates about what was happening in the congregations meant that what information did emerge relied on leaks which concentrated on in-fighting within the Italian church.

“For this reason and because the organisers of his campaign stayed largely below the radar, the Bergoglio bandwagon that began to roll during the week of the congregations went undetected by the media and to this day most [Vatican watchers] believe there was no organised pre-conclave effort to get Bergoglio elected,” Mr Ivereigh says.