LONDON (AFP/Reuters) - A sixth man was arrested Friday on suspicion of plotting acts of terrorism linked to the historic state visit of Pope Benedict XVI, British police said. Londons Metropolitan Police earlier arrested five street cleaners as part of the same investigation. Police moved quickly to make the pre-dawn arrests of the five men who worked in the area in central London near parliament where the pontiff was due to speak Friday afternoon. The BBC reported that the men had posed a possible threat to the Pope but police refused to confirm or deny that. The Vatican said the trip would go ahead as planned and that the pope was calm. The five unnamed men, aged between 26 and 50, were arrested around 5:45am (0445 GMT) on suspicion of the commission, preparation or instigation of acts of terrorism, according to a police statement. The sixth man, a 29-year-old, was arrested at around 1:45pm (1245 GMT) by counter-terror officers on suspicion of the commission, preparation or instigation of acts of terrorism, the Metropolitan Police said. The man was arrested under the Terrorism Act 2000 at residential premises in north London. He was taken to a central London police station to be interviewed by detectives. Searches are being carried out under the Terrorism Act 2000 at a total of eight residential premises in north and east London and two business premises in central London, the Met said. In addition to making the arrests, the police also searched a business in central London and homes in the north and east of the city but did not uncover any dangerous materials. The Vatican was told of the arrests as the pope was arriving at a Catholic university in southwest London. We are totally confident in police and there are no plans to change the programme, said Father Federico Lombardi. He said the pope was calm and looking forward to the rest of the visit.The police would not confirm or deny the accuracy of media reports connecting the arrests to the Popes visit. Following todays arrests the policing arrangements for the Papal visit were reviewed and we are satisfied that our current policing plan remains appropriate, they said. The Pope has been well protected during his four-day visit to Britain, travelling in a custom-built bulletproof car surrounded by security officials. The arrests follow a warning from the head of the MI5 security service that dissident Irish Republican groups opposed to British rule in Northern Ireland could seek to strike mainland Britain. Suspected Al-Qaeda plots targeting Britain originate increasingly in Somalia and Yemen, partly as a result of counter-terrorism pressure on the groups leaders in Pakistan, the head of the MI5 security service said on Thursday.