The Order of the Knights of Malta, the powerful, wealthy and mysterious Roman Catholic body that traces its origins to the Crusades, has begun a papal style search for a new leader to combat its “secretive” image after the death of its Grand Master.

Fra Andrew Bertie, 78, the first Briton to head the order and a descendant of the exiled Stuarts, died in a clinic, in Rome where the order has been based for the past 174 years. Elected Grand Master in 1988, he recently complained that the Knights’ charitable activities were overlooked by “conspiracy theorists” who suspected that its humanitarian missions in Iraq and Afghanistan were a cover for “mercenary” activities.

Last month in his traditional New Year's Day address, he said that “misinformation” about the Order of Malta was putting the lives of its volunteers “in grave danger”.

Addressing diplomats accredited to the order, he blamed “confusions created by the media, careless of verifying their sources,” which he said could have “mortal consequences.” He said: “Terrorism — or more exactly, terrorists — deliberately attack civilian populations, including women and children; they make no distinction between combatants and civilians. . . Humanitarian workers on the ground, among whom are members and volunteers of the Order of Malta, are perceived as legitimate targets. They are attacked, ransomed, kidnapped, in occurrences that are becoming more and more frequent; numbers of them have lost their lives.”

He complained that “new conspiracy theories have sprung up over recent months associating the sovereign Order of Malta with a private society of mercenaries which it is said are operating in Iraq and Afghanistan for a foreign government. These assertions have absolutely no factual basis.”

The order has 12,500 members worldwide and is run by the “Council Complete of State”, an inner core made up of some sixty “professed knights” who have taken monk-like vows of poverty, obedience and chastity.

They have begun behind-the-scenes consultations that will culminate in a conclave of the council to vote on a new Grand Master, “in about six months' time” according to insiders. Grand Masters, like Popes, are elected for life. There is no equivalent of the white smoke from the Sistine Chapel chimney however, since the votes cast are not burned but kept in the order’s archives.

Grand Masters must be able to prove “noble lineage” going back at least two centuries. “The vote is secret, and stays secret until the new Grand Master has revealed his identity to the Pope,” a source said.

Born in 1929, Bertie was educated at Oxford and the University of London and served in the Scots Guards before joining the order in 1956. He worked as a schoolteacher and a financial journalist before taking his vows in 1981. His mother, Lady Jean Crichton-Stuart, was a descendant of the Stuarts.

A charming but intensely shy man, Bertie once told The Times at his frescoed palazzo on Via Condotti near the Spanish Steps that the order had “nothing to hide”. On the other hand its procedures are arcane and aristocratic, with members wearing black robes embroidered with a white eight-pointed cross. On the order’s 900th anniversary in 1999 it, briefly, opened the doors of its complex on the Aventine Hill, where visitors can normally do no more than bend to peep through a keyhole that frames a distant view of St Peter’s.

The order, whose full title is the Sovereign Military Hospitaller Order of St. John of Jerusalem of Rhodes and Malta, has 93,000 volunteers involved in humanitarian and charity work around the world — often in conflict zones — ranging from ambulances and disaster relief to maternity hospitals and homes for disabled children. It issues its own passports and stamps, and has diplomatic relations with 99 countries and permanent observer status at the United Nations.

The order traces its origins to the 11th century when merchants from the Republic of Amalfi financed a hospital run by monks in Jerusalem to care for pilgrims to the Holy Land. The order dates its founding to 1099 when the monks took on a military role to protect the pilgrims. When the Crusaders were forced out of the Holy Land by Saladin after the fall of Acre, the order moved to Cyprus, then Rhodes and ultimately to Malta, where the knights reinforced the harbour at Valletta with the massive ramparts of Fort St Angelo, enabling them to withstand sieges by the Ottoman Turks, notably in 1565.

The Knights were eventually forced out of Malta by Napoleon, making their final move to Rome. To mark the 1999 anniversary Malta allowed the order to re-possess Fort St Angelo on a 99-year lease. The Grand Commander of the order, Fra Giacomo della Torre, was sworn in as interim head. The Grand Master, who is addressed as “Your Highness”, carries the title of prince and is considered by the Vatican to be equal in rank to a cardinal.