Pope Benedict has been accused of masterminding the child sex-abuse cover up which has rocked the Catholic Church.

Swiss theologian Fr Hans Kung has written a furious letter to the Catholic bishops accusing the Pope of engineering the global cover-up.

"There is no denying the fact that the worldwide system of covering up cases of sexual crimes committed by clerics was engineered by the Roman Congregation for the Doctrine of the Faith under Cardinal Ratzinger (1981-2005)," he said.

"During the reign of Pope John Paul II, that Congregation had already taken charge of all such cases under oath of strictest silence. Ratzinger himself, on May 18th, 2001, sent a solemn document to all the bishops dealing with severe crimes in which cases of abuse were sealed under the secretum pontificium, the violation of which could entail grave ecclesiastical penalties.

“With good reason, therefore, many people have expected a personal mea culpa on the part of the former prefect and current pope.Instead, the pope passed up the opportunity afforded by Holy Week: On Easter Sunday, he had his innocence proclaimed urbi et orbi by the dean of the College of Cardinals [Cardinal Angelo Sodano]," write Kung.

The letter was published in several publications across the world on Friday as Pope Benedict celebrated his fifth year as Pope.

In it, Kung called for another Vatican council and urged bishops to stand up for what's right.

He goes on to say that Benedict has "passed up more opportunities than" he has taken when faced with "major challenges of our time."

He gives examples of such missed opportunities. “Rapprochement with the Protestant churches”, “reconciliation with the Jews”, “the opportunity for a dialogue with Muslims”, and “reconciliation with the colonised indigenous peoples of Latin America”.

He continues, “the opportunity to help the people of Africa by allowing the use of birth control to fight overpopulation and condoms to fight the spread of HIV” and that of making “peace with modern science by clearly affirming the theory of evolution and accepting stem-cell research."