Leading peer and QC Baroness Helena Kennedy has spoken of the "huge compassion" she feels towards Cardinal Keith O'Brien following his admission that his sexual conduct had "fallen beneath the standards" expected of him.

Lady Kennedy, who was brought up in Glasgow as a Roman Catholic, said it was "torture" for the Church to force priests who wanted to have a sex life to be celibate as she spoke at a news conference calling for reform of the Catholic Church.

"I feel very sad for Cardinal O'Brien because here was a man who quite clearly had wanted to have a sexual life and felt that it was a failing for him to want to have a sexual life and that he was going against his commitment to celibacy," she said.

"It is terrible to torture people by expecting that of them and I just feel huge compassion for him. I do not like the idea that there might be an issue of being predatory but I do not want to make a judgment on that.

"But he himself has said that he was involved in sexual activity and I feel very sad that that was something that he had to in some way bury, then give expression to - then feel shame and guilt and presumably is absolutely covered with guilt now.

"I feel very sad for him and for his victims."

Lady Kennedy's remarks come after Cardinal O'Brien resigned last week from his post as Archbishop of St Andrews and Edinburgh amid allegations of "inappropriate behaviour" towards three serving priests and one former priest.

This weekend Cardinal O'Brien admitted that his sexual conduct had "fallen beneath the standards" expected of him and asked forgiveness of those he had offended.

In a statement, he said: "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."

Lady Kennedy was speaking at the launch in the House of Commons of the Catholic scholars declaration on authority in the Church.

The group has said that the faithful have suffered from "misguided" church rulings on sexual ethics, including contraception, homosexuality and remarriage. It has called for a new pope to introduce more democracy in the Church.

Lady Kennedy told the news conference that she backed the Catholic Church's work in areas such as alleviating poverty and also its stance on opposing the Iraq war.

But she said there had been "serious crises" in the Catholic Church and it faced issues of "transparency, accountability and governance.

"The Church has existed for millennia and like all ancient institutions it is very slow to change and it is confronted with a number of problems," she said.

"It is almost exclusively run by men and that is how the world was, we don't have to see it as a conspiracy, it was the nature of things," she said.

"We have to recognise that within the Catholic Church power is located in one gender, we might dress up the story of women playing important roles in the Church but it is actually a fiction and is unacceptable in the modern world.

"That issue of women's absence from the positions of power within the Church I do think creates a serious dysfunction for the Church."

Lady Kennedy said she was opposed to compulsory celibacy for the priesthood, saying it should be a choice. Women should also be permitted to become Catholic priests, she said.

"I think we as people who are part of this Church recognise that there is a wholly disproportionate, if you like, distraction about sex, it arises on many different fronts, the unwillingness to accept that in relationships people give expression to their love in many different ways, that there is nothing that is unhealthy about having a sexual drive.

"Unfortunately, we still cling to this idea that sex really is about reproduction."

Lady Kennedy said she was not speaking as someone who would consider herself to be a "devout" Catholic. She said she preferred to call herself a "bad" Catholic.

"I call myself a bad Catholic, I say that I am a bad Catholic... that is my declaration because I don't feel that the Church is in any way reflecting the things that are the concerns of many of the women who are brought up as Catholics," she said.

"The is the reason why so many young people are no longer practising Catholics, we don't feel that the Church in any way is engaging with the issues that concern them."

Speaking about the term "devout" to describe Catholics, she said: "The word for me is often a description of people who I think, do less credit to the Church."

She added that the Church had failed in its investigation of child sex abuse.