Cardinal Keith O'Brien's resignation casts shadow over Papal Conclave One of Scotland's most eminent historians described Cardinal O'Brien's resignation as "probably the gravest single public crisis" for the Scottish Catholic Church since the Reformation. There were predictions that the allegations, if true, would shatter its moral credibility and demoralise the faithful. The Cardinal has said he will be "contesting" the allegations, published in The Observer at the weekend, and is consulting lawyers. In a statement, the normally plain-spoken cleric said simply: "For any good I have been able to do, I thank God. Four men - three priests and one former priest - have accused him of "inappropriate" behaviour dating back as far as 1980, before he was Archbishop. Their claims are particularly damaging given his vehement denunciations of homosexuality. He has described gay marriage as a "grotesque subversion." The Cardinal was due to retire and had already tendered his resignation to the Pope, citing "indifferent health," but no date had been set. Yesterday the Pope confirmed that it would take immediate effect. The Cardinal said: "The Holy Father has now decided that my resignation will take effect today." In one of his last acts before stepping down himself, the Pope will put an "Apostolic Administrator" in charge of the archdiocese until a new Archbishop is appointed. The Cardinal thanked the Pope for his "kindness and courtesy" in the past, adding: "I also ask God's blessing on my brother cardinals who will soon gather in Rome to elect his successor. I will not join them for this conclave in person. Writing for telegraph.co.uk, Prof Tom Devine, an authority on Scottish history, said: "This is probably the gravest single public crisis to hit the Catholic Church in Scotland since the Reformation and its effects in the short term are incalculable. Many of the faithful in Scotland will be stunned by the seismic turn of events. But the Cardinal's personal chaplain, Mgr Thomas Chambers, said: "The Church is over 2,000 years old - it's survived a lot. So we'll come through this together. In Rome, officials declined to acknowledge Cardinal O'Brien's decision to step aside from the conclave. Support groups for victims of paedophile priests renewed calls for others to stand aside as well. Los Angeles's retired Cardinal Roger Mahony, Philadelphia's former Archbishop Justin Francis Rigali, the Belgian Cardinal Godfried Danneels and Ireland's Cardinal Sean Brady, have all faced allegations relating to abuse being covered up. Robert Mickens, Rome correspondent for The Tablet, a Catholic magazine, said: "They don't like to set precedents like that but that is why it is very interesting what has happened with O'Brien. We don't know whether it was coordinated, if the Holy See has okayed this or even demanded it. All I can say is that it looks very, very strange, the timing of this. Michael Walsh, author of The Cardinals, said: "Other people will be under greater pressure to stay away. There has been nothing like this before. It is almost as if the fact that the Pope resigned rather than dying in office has created a degree of instability in the Catholic Church. Ambrogio Piazzoni, a Vatican historian, said that any decision by a cardinal to stay away would have to be approved by the full College of Cardinals.