Police sources say officers think there was "no credible threat" to the Pope after six arrested men were questioned.
Searches have finished without the discovery of anything significant.
The six - who work as street cleaners in Westminster - were arrested after they were overheard in the works canteen apparently plotting an attack.
The Metropolitan Police has refused to confirm reports that the men were joking, saying they had to investigate what might have been a genuine threat.
The men are employed by Veolia Environment Services, a cleaning company contracted by Westminster Council.
At least five of the men are not British nationals. Most are thought to be Algerian.
The men, aged between 26 and 50, were arrested on suspicion of the commission, preparation or instigation of acts of terrorism on Friday.
Armed officers arrested the first five men at the company's Chiltern Street depot in west London as they were preparing to go on shift. A sixth man was later taken into custody.
Police officers searched eight homes in north and east London and two business premises in central London, including a street cleaning depot.
Searches of the premises had now been completed and had not revealed any weapons or suspicious materials.
In the statement, the Metropolitan Police said policing arrangements for the papal visit were reviewed following the arrests, and that police were satisfied that the current policing plan for the Pope's visit remained appropriate.
"The itinerary has not changed. There is no change to the UK threat level," the statement added.
The current official threat level in the UK is "severe", which means that security chiefs believe a terror attack is "highly likely".
In all, the policing bill for the papal visit is expected to top £1m.