Pope Benedict XVI presides over a Celebration of Catholic Education at St Mary’s University College in London on Friday. Benedict is on the second day of a four-day visit, the first-ever state visit by a pope to Britain.

London ? Police raided a garbage depot and arrested street cleaners in a suspected terror plot against Pope Benedict XVI on Friday. Undeterred, the pontiff stuck to his message, reaching across Britain’s religious and secular divide to demand a greater role for faith in public life.

Despite the six arrests, the pope did not alter a schedule rich in symbolism in this officially Protestant country with a history of anti-Catholicism: He prayed with the Archbishop of Canterbury and became the first pope to worship in Westminster Abbey.

Benedict also addressed political, cultural and business leaders in Westminster Hall, for centuries the center of British political life, asserting “the legitimate role of religion in the public square.”

Among those in attendance were Tony Blair — a prominent convert to Catholicism — as well as former Prime Ministers Margaret Thatcher, John Major and Gordon Brown.

Faith, the pope said, “is not a problem for legislators to solve, but a vital contributor to the national conversation.”

Benedict was informed of the pre-dawn arrests while visiting a Catholic college, the first stop on the busy second day of his state visit.

Five of the suspects were street cleaners arrested at a garbage depot in central London and a sixth was picked up later in the day. All six were arrested “on suspicion of the commission, preparation or instigation of acts of terrorism.” Police said they ranged in age from 26 to 50, and media reports said some were Algerian, though authorities would not confirm that.

Police said they received information about a potential threat against the pope overnight, prompting the arrests under Britain’s Terrorism Act. All six were being questioned and had not been formally charged.

At the scene of the street cleaners’ arrests in Chiltern Street, near the famed Madame Tussauds wax museum, police cordoned off part of the road. Police officers, some dressed in white protective overalls, removed items from the depot, and examined garbage cans.

The street cleaners worked for a contractor on behalf of Westminster Council, the authority responsible for much of central London, including the Houses of Parliament, Westminster Abbey and other sites on the pope’s itinerary Friday. However, the arrests took place at a depot responsible for cleaning another part of the city.

A street sweeper at the depot said at least one of those arrested was Algerian and he believed all five were from North Africa. He spoke on condition of anonymity because he was not authorized to talk to the media.

There have been no known plots against Benedict in his five-year papacy. His predecessor, Pope John Paul II, was gravely wounded in a 1981 assassination attempt.

Benedict’s visit has been overshadowed by disgust over the Catholic Church’s clerical abuse scandal and opposition from secularists and those who oppose the church’s positions on homosexuality and using condoms to fight AIDS.

Security has been visibly higher than on Benedict’s previous foreign trips, and Vatican officials have acknowledged that Britain represents a greater threat than other European countries the pope toured this year, including Portugal, Malta and Cyprus.

News of the arrests came as the pope was meeting representatives of other religions, including Muslims and Jews. He stressed the importance of mutual respect, tolerance and freedom to follow one’s conscience.