|Hundreds of protesters have been demonstrating against the Pope's four-day visit to Britain [AFP]
British police say they have arrested six men on suspicion of preparing an attack at the same time as Pope Benedict XVI tours the country.
Five of the men, aged between 26 and 50, were detained under the Terrorism Act at business premises in central London, police said in a statement on Friday. A sixth was arrested later at a home in north London, police said.
At least five of the men were working as cleaners for Veolia Environmental Services, a contractor used by Westminster City council.
The council is responsible for areas of the capital where the pope was spending part of Friday, including the Houses of Parliament and Westminster Abbey.
Searches are being carried out at other business and residential buildings in the capital, after police received information leading to the arrests.
Police did not specificy that the men were plotting against the pope, but authorities said security arrangements for the pontiff had been reviewed.
"Following today's arrests, the policing arrangements for the papal visit were reviewed and we are satisified that our current policing plan remains appropriate," London's Metropolitan Police said in
Frederico Lombardi, a spokesman for the Vatican, said the pope was not in fear of a threat.
"The pope has put complete trust in the police. It is not necessary to change any plans. The situation is not particularly dangerous," he told journalists in London.
"When we were in Sarajevo the situation was much more dangerous. The pope is happy and calm."
The pope has been travelling in a custom-built bulletproof car surrounded by security officials as he conducts a four-day visit to the UK, in the country's first state visit by a Roman Catholic pope.
'Marginalisation of religion'
The pope warned on Friday against the "marginalisation of religion" as he delievered a keynote speech to an audience of politicians and senior figures in Westminster Hall, the historic heart of the Houses of Parliament.
Speaking on the second day of his visit, Benedict said that there were also "worrying signs" that religion's role in public life was diminishing.
Having warned at the start of his state visit on Thursday of "aggressive secularism" in Britain, Benedict returned to the theme in the speech to guests including Margaret Thatcher, Tony Blair, Gordon Brown and John Major, all former UK prime ministers.
"I cannot but voice my concern at the increasing marginalisation of religion, particularly of Christianity, that is taking place in some quarters, even in nations which place a great emphasis on tolerance," the pope said.
"There are those who argue that the public celebration of festivals such as Christmas should be discouraged, in the questionable belief that it might somehow offend those of other religions or none."
Following the speech, the pope held joint prayers with Rowan Williams, the Archbishop of Canterbury and head of the Church of England, in a symbolic act of unity at London's Westminster Abbey.
Earlier, Benedict had met with Dr Williams at Lambeth Palace, the archbishop's official residence in London.
Benedict has a delicate path to tread in England and Scotland in relations with the Anglican church after his offer last October making it easier for disaffected Anglicans, unhappy over the ordination of women and gay bishops, to convert.
The archbishop said that the pope was "most welcome" at the palace.
The pope began his schedule on Friday at a school in Twickenham, south London.
Hundreds of protesters angry over the Catholic Church sex abuse scandal gathered outside the school, where the pope held a "big assembly" children from around Britain.
In his address to the crowd, the pope said the church's first priority was to provide a "safe environment for children and young people".