Archbishop Peter Smith of Southwark has warned Catholic families that "crackpots and lunatics" could still disrupt the papal visit.
The archbishop said Protest the Pope campaigners had promised in a meeting last week that they would not disrupt any of the ceremonies during the visit.
But he said the protesters could not guarantee that "some lunatic might not attach themselves to some of their events".
"To be fair to them nobody can guarantee that you are not going to get crackpots and lunatics tagging on to these things and acting individually,” he said.
