The crisis engulfing the Catholic Church deepened as the outgoing Pope effectively sacked Britain's most senior cleric, who has been accused of inappropriate behaviour towards young priests.
Cardinal Keith O'Brien apologised to "all whom I have offended", but his immediate removal from office means he will not now travel to Rome to choose a successor to Pope Benedict XVI - an attempt by the Vatican to prevent the occasion being overshadowed by further scandal.
The Vatican faces mounting pressure to ban other cardinal electors tainted by claims of sexual misdeeds.
O'Brien is the first Catholic clergyman of the highest rank to be forced out since Cardinal Groer in 1998, when the Austrian apologised but did not admit molesting youths at a monastery in the 1970s. It was alleged that attempts by the then Cardinal Joseph Ratzinger to investigate were blocked by Pope John Paul II.
The conclave to choose a new Pope could now start as early as this week after Benedict again defied convention by scrapping the 15-day waiting period between pontiffs.
O'Brien's resignation was welcomed by gay rights campaigners, who have been enraged by the 74-year-old Archbishop of Edinburgh's strident opposition to same-sex marriage.
As leader of Scotland's Catholics and Britain's only cardinal elector, his resignation means Britain will have no say in the choice of the next leader of the world's 1.2 billion Catholics.
Although he has not spoken publicly on the issue, it is understood that O'Brien continues to contest allegations from the 1980s that he made unwanted advances to four members of the clergy, including three current priests.
An investigation is under way into the claims, which resulted in one of the men requiring long-term psychological counselling.
O'Brien said the Pope had initially accepted his resignation last November but it was due to take effect to coincide with his 75th birthday next month. Cardinals under 80 are still entitled to attend the conclave to vote.
However, after weekend newspaper revelations, he said: "The Holy Father has now decided that my resignation will take effect today and that he will appoint an apostolic administrator to govern the archdiocese in my place until my successor as archbishop is appointed. I do not wish media attention in Rome to be focused on me - but rather on Pope Benedict XVI and on his successor."