Cardinal Keith O'Brien tonight admitted that his sexual conduct had at times "fallen below the standards expected of me as a priest, archbishop and cardinal".

The cardinal, who was Britain's most senior Catholic cleric, stepped down from his post as Archbishop of St Andrews and Edinburgh last week, a day after three priests and a former priest made allegations of "inappropriate" behaviour against him.

In a statement issued by the Catholic Church in Scotland tonight, he apologised and asked forgiveness from those he had "offended".

The statement read: "In recent days certain allegations which have been made against me have become public. Initially, their anonymous and non-specific nature led me to contest them.

"However, 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.

"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."

It is understood he is currently out of the country and will not be attending the Conclave to elect the successor to Pope Benedict. His absence means that the church in Britain has no vote in the process.

On Monday it was announced that Cardinal O'Brien would resign his post with immediate effect.

That move came a day after it was reported that three priests and a former priest had complained about him to the Vatican over alleged "inappropriate" behaviour stretching back 30 years.

The cardinal, who initially said he was taking legal advice when the allegations against him emerged, had been due to retire later this month when he turned 75.

In an earlier statement issued via the Catholic Church's media office in Scotland, the cardinal said: "For any failures, I apologise to all whom I have offended."

In fresh claims published today, the former priest who reported Cardinal O'Brien to the Vatican over the allegations of "inappropriate" behaviour attacked the church's response to the complaints.

The man, who remains anonymous, said he had been "disappointed" by the church's reaction.

He said: "There have been two sensations for me this week. One is feeling the hot breath of the media on the back of my neck and the other is sensing the cold disapproval of the church hierarchy for daring to break ranks. I feel like if they could crush me, they would.

"The vacuum the church has created has allowed whimsy and speculation to distort the truth, and the only support I have been offered is a cursory email with a couple of telephone numbers of counsellors hundreds of miles away from me."

Another priest called for the Catholic Church in Scotland to be more open in dealing with complaints.

Father John Robinson said: "If the Catholic Church in Scotland is to heal itself, we need transparency and understanding.

"We need to learn lessons from the mistakes we have made in the past and move on to become a more loving and understanding church which does not condemn victims or even abusers."

The allegations against the cardinal emerged just days after he called for the Catholic Church to end its celibacy rule for the priesthood.

He said that many priests struggle to cope with celibacy and should be allowed to marry if they wish.

Cardinal O'Brien, who recently advocated priests marrying, has been an outspoken opponent of plans to legalise same-sex marriage.

Last year his stance earned him the Bigot of the Year award from the gay rights group Stonewall.

The cardinal, who was born in Ballycastle, Co Antrim, had been the Archbishop of St Andrews and Edinburgh since 1985.

Ordained as a priest in 1965, he was proclaimed a cardinal by Pope John Paul II in October 2003.

The archbishop who is temporarily replacing Cardinal O'Brien recently spoke of the "pain and dismay" he shares with worshippers as he took Mass for the first time since being appointed.

Archbishop Philip Tartaglia told those gathered at St Mary's Cathedral in Edinburgh last week that he understands that the archdiocese is in a "state of shock for the loss of its shepherd" following the cardinal's resignation.

The Pope appointed the Archbishop of Glasgow to govern the Roman Catholic Archdiocese of St Andrews and Edinburgh until a permanent replacement is chosen.