On the eve of the 80th anniversary on Thursday of the founding of the conservative Roman Catholic organisation Opus Dei, a leading Catholic writer has claimed that the prelature has benefited rather than suffered from the controversy over Dan Brown's The Da Vinci Code.

Vittorio Messori, who has collaborated on books with both Pope Benedict XVI and his predecessor, John Paul II, said that on the verge of its 80th birthday Opus Dei could count on over 85,000 members "in all continents", 98 per cent of them lay people.

He said that while some considered Saint Josemaria Escrivá de Balaguer, the founder of Opus Dei, a "megalomaniac", others saw his life and testimony as one of humility. Writing in the Italian daily Corriere della Sera, Mr Messori said that the "tsunami" set off by the book and film of The Da Vinci Code had been thought by many to have caused "irreparable damage" to the image of Opus Dei.

In reality, however, Opus Dei had responded not only with protests but also with its own "information campaign", which had been so effective that it was now studied in US journalism schools. The result had been not only praise for the prelature's stance of "elegant understatement" but also a rise in the number of adherents. This had been helped by Mr Brown's errors, such as making his Opus Dei assassin a monk when Opus Dei is not a monastic order and has no monks, Mr Messori said.

Opus Dei (The Work of God) teaches that everyone is called to sanctity through their daily lives. Founded in Spain on October 2 1928, when Josemaria Escrivá said he experienced a "vision" in which he "saw" Opus Dei, it was approved in 1950 by Pope Pius XII. John Paul II made it into a personal prelature in 1982.

Critics say it is secretive and elitist, with arcane rituals for some members including mortification of the flesh. However Josemaria Escrivá was canonised in 2002 by John Paul II, and in 2005 Pope Benedict blessed a statue of him in an outside niche of St Peter's Basilica.