Pope Benedict XVI wrapped up an emotional day in London with a prayer vigil that drew 80,000 to Hyde Park.
The vigil capped a day in which the pope met and prayed with victims of priestly sexual abuse while thousands of people opposed to his visit marched in central London in the biggest protest of his five-year papacy. He also led a Mass at Westminster Cathedral.
At the vigil, he praised Cardinal John Henry Newman, a 19th century convert from Anglicanism whom the pope wants to hold up as a model for the faithful. On Sunday he was scheduled to lead a Beatification Mass at Cofton Park Birmingham for Newman.
The pope also plans to meet with the bishops of England, Scotland and Wales before he leaves for Rome.
Bill Kilgallon, chairman of the National Catholic Safeguarding Commission — a church group that organized the encounter — said five people met with the pontiff for about 30 or 40 minutes Saturday at the Vatican's ambassador's residence in Wimbledon.
The pope expressed "his deep sorrow and shame over what the victims and their families suffered," according to a Vatican statement.
Vatican spokesman Rev. Federico Lombardi said the pontiff was "moved by what they had to say and expressed his deep sorrow and shame."
The Vatican statement was similar to ones it issued after Benedict met with abuse victims over the past two years while visiting the United States, Australia and Malta. But continued revelations of abuse — the latest in Belgium — have failed to placate critics demanding that the pope and other Vatican officials take personal responsibility and crack down on bishops who covered up abuses by their clerics.
As the Vatican issued the statement, up to 20,000 chanting demonstrators snaked though the streets of London to protest against his handling of the abuse crisis and his views on homosexuals and the ordination of women.
Moving towards the prime minister's residence at Downing Street, the protesters 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 Birmingham.
The pope celebrated a Mass on Saturday 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 words in a sermon there were the 83-year-old pontiff's 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.
Still, victims said they were not satisfied, with one group named Bishops Accountability 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.
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.
It was during Harman's tenure as a minister in the previous Labor government that the pope condemned an equality bill going through parliament that would have forced churches to hire homosexuals or transsexuals. The provision was later defeated.
Clegg is a professed atheist but is married to a Spanish Roman Catholic who is raising their children in the Church.
Arrests in plot
On Saturday, six men arrested in London on suspicion of preparing an attack were freed after Scotland Yard determined there was no credible threat to the pope. Police searched eight homes and two businesses and reviewed their security operation.
British broadcaster Sky cited unnamed sources as saying the six were Algerian.
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.
The Associated Press and Reuters contributed to this report.