LONDON, (AFP) – British police have arrested five street cleaners on suspicion of plotting a “terrorist” attack linked to the historic state visit of Pope Benedict XVI, officials said on Friday.

The Vatican insisted that the pope was “calm” following the arrests and that it had full confidence in Scotland Yard’s ability to protect him.

The five men, aged between 26 and 50 and reportedly Algerian, were questioned “on suspicion of the commission, preparation or instigation of acts of terrorism” at around 5:45 am (0445 GMT).

Reports said they were just about to leave their depot to start a shift cleaning streets in the London borough of Westminster where Benedict was spending much of Friday, speaking at the Houses of Parliament and attending a service with Archbishop of Canterbury Rowan Williams at Westminster Abbey.

Britain’s former prime ministers Tony Blair and Margaret Thatcher are among those also expected to attend the service, billed as a highly public show of unity between the Anglican and Catholic leaders.

Police insisted that the policing arrangements for the pope’s visit would not change despite the arrests.

“Following today’s arrests the policing arrangements for the papal visit were reviewed and we are satisfied that our current policing plan remains appropriate,” a Scotland Yard statement said. “The itinerary has not changed.”

But security was tight in Westminster, with hundreds of police on the streets, some with sniffer dogs, and barricades were being set up.

Vatican spokesman Federico Lombardi added: “We’re totally calm, the pope is happy… we’re totally confident in the work of the police.”

Westminster City Council confirmed the five men worked for environmental services company Veolia, which the council contracts to keep the streets clean.

Police were searching the central London business address where the men were arrested plus two houses in the British capital but reported they did not find any “hazardous items” in initial checks.

The alert came on the second of four days of the first ever papal state visit to Britain, for which the huge security operation is costing up to 1.5 million pounds (2.3 million dollars, 1.8 million euros).

As well as the Westminster Abbey service and address at parliament’s historic Westminster Hall, Benedict was also due to meet with Williams at Lambeth Palace, the Anglican archbishop’s London residence.

It was a day of firsts for the 83-year-old pope — no pontiff has visited Lambeth Palace or the historic abbey since the foundation of the Church of England when king Henry VIII broke with Rome in 1534.

The engagements come just 11 months after Benedict shocked the religious world with an offer to take in dissident Anglicans angered by their church’s moves to consecrate female bishops.

At Westminster Abbey, the pope will be welcomed by the canon, Reverend Jane Hedges, a prominent Church of England figure and campaigner for the ordination of women, in a meeting seen as controversial as the Vatican considers female ordination a “crime against the faith”.

The run-up to the pope’s visit to Britain was clouded by criticism of the Catholic Church’s handling of child abuse by priests and a furore over the 20 million pound cost.

On the first day of his visit, the pope warned of the risk of “aggressive secularism” in Britain and greeted tens of thousands of people at a mass in Glasgow and on the streets of Edinburgh.

The pope has also made some of his clearest condemnations yet of the sexual abuse of children by priests, saying the Catholic Church was not “vigilant” enough about the problem and insisting the revelations of paedophilia “were a shock to me”.

Benedict hinted at the scandal Friday, saying in a speech at a college in Twickenham, southwest London, that it was the job of Catholic schools to provide “a safe environment for children and young people”.

He is expected to meet a group of 10 victims of abuse on Friday or Saturday in London.

Benedict will travel to the English city of Birmingham on Sunday to preside over the beatification of a 19th century cardinal, John Henry Newman, an Anglican who converted to Catholicism, in the climax of the visit.