London, England (CNN) -- Pope Benedict XVI praised Britain Sunday for standing up to the Nazis, a remark that could rekindle controversy over the pope's past -- reminding listeners that he was forced as a young man to join the Hitler Youth.

Describing himself "as one who lived and suffered through the dark days of the Nazi regime in Germany," the German-born pontiff said it was "deeply moving... to recall how many of your fellow citizens sacrificed their lives, courageously resisting the forces of that evil ideology."

Later in the day, in an address to the UK's Catholic bishops, the pope invoked the church sex abuse crisis, saying it "seriously undermines the moral credibility of church leaders."

But it was the comment about his youth that was a break from Benedict's usual practice, CNN Senior Vatican Analyst John Allen said.

"Unlike John Paul II, Benedict doesn't usually play on his own biography, so when he does it's always to make a point," he said.

Unlike in remarks to Queen Elizabeth II on Thursday, when he mentioned the Nazis in a much less personal way, "today was a Mass, speaking directly to the people," Allen said. "I think Benedict felt it was important, as a German pope, to thank the British for standing up to a tyranny that his own country produced and that touched his own early life."

He was speaking at the religious climax of his historic four-day trip to Britain, the beatification of Cardinal John Henry Newman, a towering 19th century religious thinker. Beatification is the last step before sainthood.

Pope Benedict XVI has been making a public case against "aggressive secularism" during his trip to Scotland and England, but the state visit has been been shadowed by anger over the abuse of children by Catholic clergy and the arrest of six men suspected of plotting an attack against the pope.

The men were released without charge early Sunday morning, after having been detained on Friday, police said.

In his Sunday speech to bishops, the pope devoted a part of his message to the abuse scandal, which included a reminder that he now speaks somewhat regularly about the crisis.

"I have spoken on many occasions of the deep wounds that such behaviour causes," he said, according to a copy of his speech distributed by the Vatican, "in the victims first and foremost, but also in the relationships of trust that should exist between priests and people, between priests and their bishops, and between the Church authorities and the public."

Benedict indicated that he is satisfied by the bishops' response to the scandal, though that response has been criticized as inadequate by some victims' groups.

"I know that you have taken serious steps to remedy this situation, to ensure that children are effectively protected from harm and to deal properly and transparently with allegations as they arise," the pope said Sunday. "You have publicly acknowledged your deep regret over what has happened, and the often inadequate ways it was addressed in the past."

In a speech shortly before the pope's departure Sunday afternoon, British Prime Minister David Cameron said the pontiff's visit marked "an incredibly moving four days for our country... (a) truly historic first State Visit to Britain."

"You have offered a message not just to the Catholic Church, but to each and every one of us, of every faith and none," Cameron said, according to a copy of his remarks distributed by his office.

On Saturday, Benedict met with five victims of abuse, the Catholic Communications Network said, the same day the pope expressed his "deep sorrow" for the scandal that has rocked the Catholic Church.

But his acknowledgement of the abuse suffered by children within the church -- the first time he publicly addressed the issue during his four-day trip to Britain -- was not enough to dissuade thousands of protesters from expressing their anger on the streets of London.

Thousands gathered Saturday near Hyde Park, the site of an afternoon prayer vigil led by the pope for the beatification of Newman, a Catholic convert who died in 1890 and is credited with helping rebuild Britain's Catholic community.

A wide variety of sometimes expletive-laced signs could be seen dotting the crowd of demonstrators, which included atheists, clergy abuse victims and gay rights campaigners. One poster accused the pope of being the boss of the "world's largest sex gang." Another sign asked if he "fancied the baby Jesus."

The protests came hours after the pope addressed the abuse scandal during Mass at Westminster Cathedral.

"I think of the immense suffering caused by the abuse of children, especially within the church and by her ministers," he said. "Above all, I express my deep sorrow to the innocent victims of these unspeakable crimes, along with my hope that the power of Christ's grace, his sacrifice of reconciliation, will bring deep healing and peace to their lives.

"I also acknowledge with you the shame and humiliation which all of us have suffered because of these sins; and I invite you to offer it to the Lord with trust that this chastisement will contribute to the healing of victims, the purification of the church, and the renewal of her age-old commitment to the education and care of young people.

"I express my gratitude for the efforts being made to address this problem responsibly, and I ask all of you to show your concern for the victims and solidarity with your priests."

Later Saturday, the pope met with victims of clerical sexual abuse, according to the Catholic Communications Network, the media office of the Bishops' Conference. Three of the victims were from Yorkshire, one from London and one from Scotland, the network said said.

The pope also met Saturday with people involved in the National Catholic Safeguarding Commission at St. Peter's Residential Home in Vauxhall, London.

A board member of SNAP, the Survivors Network of those Abused by Priests, expressed hope that the outcome of the victims' meeting will be positive.

"We hope each of these brave individuals feels better as a result of the meeting, both now and years from now," board member Mark Serrano wrote in a statement. "It takes real courage to disclose your pain to others, especially those in authority. We hope the risk these victims have taken will prove to be fruitful, for them, for other victims and for children being molested today and in the future."

But Serrano also echoed other SNAP members' statements made earlier in the day, noting that the pope needs to take action against abuse, not just make apologies for it.

"Today's meeting is more of the same from the pope: all talk, no action," he wrote. "With literally the stroke of a pen, of course, he could radically change deeply-rooted, centuries-old destructive patterns of recklessness, callousness and deceit within the Catholic hierarchy that have directly led to hundreds of thousands of trusting children and vulnerable adults being raped, sodomized and fondled by clerics. But he refuses."

CNN's Richard Allen Greene, Melissa Gray, Carol Jordan and David Wilkinson contributed to this report.