LONDON (Reuters) - Pope Benedict made one of his strongest apologies to victims of sexual abuse by Roman Catholic priests on Saturday in London, while thousands of marchers staged the biggest protest of any of his trips abroad.
As he has done on three previous visits, the pope held a private meeting with victims of sexual abuse hours after telling worshippers at a Mass that pedophile priests had brought "shame and humiliation" on him and the Roman Catholic Church.
"He was moved by what they had to say and expressed his deep sorrow and shame over what victims and their families had suffered," a Vatican statement said after the meeting five British adults who were abused as children.
"He prayed with them and assured them that the Catholic Church is continuing to implement effective measures designed to safeguard young people, and that it is doing all in its power to investigate allegations, to collaborate with civil authorities and to bring to justice (those) ... accused of these egregious crimes," said the statement.
It was nearly identical to those issued after past meetings.
As the meeting took place, some 10,000 chanting demonstrators snaked through the streets of London to protest against his handling of the abuse crisis and his views on homosexuals and the ordination of women.
They carried banners reading "Benedict's homophobia costs lives" and "Protect the Children - Demote the Pope." It was the largest demonstration so far on the pope's four-day visit to Britain -- which ends on Sunday in the city of Birmingham -- and the largest of any of his 17 trips abroad.
In the early evening, he was driven past some of London's landmarks, including Buckingham Palace, as tens of thousands of people cheered him on his way to a prayer vigil in Hyde Park, where some 80,000 people had gathered.
He began the day with a Mass for some 2,000 people in Westminster Cathedral, the mother church for Roman Catholics in England and Wales and a symbol of the struggle of Catholics to assert their rights after the Reformation.
His apology in a sermon there was his latest attempt to come to grips with the scandal that has rocked the 1.1 billion-member Church, particularly in Europe and the United States.
"I think of the immense suffering caused by the abuse of children, especially within the Church and by her ministers. Above all, I express my deep sorrow to the innocent victims of these unspeakable crimes ...," he said in his sermon in the towering cathedral built in the late 19th century.
SHAME AND HUMILIATION
"I also acknowledge with you the shame and humiliation that all of us have suffered because of these sins," he said, adding that he hoped "this chastisement" would contribute to the healing of the victims and the purification of the Church.
He has apologized before for sexual abuse by priests and has acknowledged that the Church was slow to deal with the problem. But his comments on Saturday were among his most direct.
Groups defending victims were not satisfied, with one group named Bishop.Accountability.org calling it "public relations not penitence."
"An apology is what a schoolboy does when he kicks a football through a window. What we need is for the pope to release all the files on predator priests," Sue Cox, a demonstrator who was abused as a child, said on television.
During a visit to an old age home run by Catholic nuns, he spoke to a group of lay people who oversee the implementation of child protection measures and told them it was important that "any allegations of abuse are dealt with swiftly and justly."
The pope began his last day in London by holding separate meetings with Prime Minister David Cameron, deputy Prime Minister Nick Clegg and acting opposition leader Harriet Harman.
Clegg is a professed atheist but is married to a Spanish Roman Catholic who is raising their children in the Church.
On Friday, anti-terrorism police, on high alert for the pope's visit, arrested six men in London on suspicion of preparing an attack. Police searched eight homes and two businesses and reviewed their security operation.
On Saturday night, the BBC, quoting police sources, reported that after a day of interrogations, the police concluded that there had been "no credible threat" to the pope.
On Sunday he flies to Birmingham in central England, where he will beatify Cardinal John Henry Newman, one of the most prominent English converts from Anglicanism to Catholicism.