The former head of the Catholic Church in Scotland has admitted his sexual conduct had "fallen below the standards expected of him".

Cardinal Keith O'Brien, who was Britain's top-ranking Catholic, resigned on February 25 one day after a newspaper reported that three priests and one former priest had complained about his conduct towards them back in the 1980s.

In a statement issued by the church on Sunday, Cardinal O'Brien apologised and asked for forgiveness after appearing to admit to sexual misconduct.

"I wish to take this opportunity to admit that there have been times that my sexual conduct has fallen below the standards expected of me as a priest, archbishop and cardinal," he said in the statement posted on the Scottish Catholic media office website.

"To those I have offended, I apologise and ask forgiveness. To the Catholic Church and people of Scotland, I also apologise.

"I will now spend the rest of my life in retirement. I will play no further part in the public life of the Catholic Church in Scotland."

Cardinal O'Brien's retirement as the Archbishop of St Andrews and Edinburgh came after The Observer Sunday newspaper reported the priests' complaints over incidents dating back to the 1980s.

The cardinal initially rejected the allegations and said he was seeking legal advice.

But he said he was ruling himself out of the conclave to elect the next pope to avoid focusing media attention on himself.

Last year Cardinal O'Brien labelled gay marriage "a grotesque subversion" landed him with a 'Bigot of the Year' award from gay rights group Stonewall.

The cardinal's dramatic resignation and self-exclusion from the conclave added to a sense of crisis in the Catholic Church as it deals with the resignation of Pope Benedict against a backdrop of scandals.

Cardinal O'Brien would have been Britain's only elector at the conclave.

ABC/Reuters