Protesters have scaled Westminster Abbey claiming fathers are being "crucified" by the courts over access to their children.
The protesters climbed about 40ft up the abbey
Two members of the group, called Real Fathers for Justice, climbed about 40ft up the abbey with a dummy on a cross.
A spokesman for the Abbey, one of the world's most famous churches, said he hoped it would not interfere with services over Easter.
The original Fathers 4 Justice group disbanded in January.
Police were called at 0900 BST to the abbey and were "attempting to bring this matter to a safe conclusion".
A spokesman for the Dean and Chapter of Westminster Abbey said the protesters were 35ft up on a balcony on the West Tower.
He added: "We understand and want to defend the right of legitimate protest, but would be disappointed if such a protest interfered with worship for thousands of members of the public over the holy week.
"On another occasion we would be happy to listen to views presented in a calm and rational way."
Services are going ahead, although access through the West Front is not possible while the protest continues.
For three years the original Fathers 4 Justice group carried out audacious stunts to highlight the cause of men denied access to their children.
Protests included packages of purple flour hurled at Tony Blair in the Commons, and a man dressed as Batman staging a five-hour protest on a balcony at Buckingham Palace.
But it disbanded in January, following newspaper reports that fringe members were said to have talked about holding the prime minister's young son to highlight their cause.
It is thought Thursday's protest had been intended to be a costumed stunt.
A spokesman for Real Fathers for Justice said: "They had Roman soldier costumes, but the police have snatched them."