Staff at St Paul's have been force to clean up human waste from inside the cathedral, a report in a newspaper has claimed.
The waste has appeared on a carpet inside the church, near to the West Steps, several times in recent weeks, according to staff, who say whoever is to blame is using the church as a "latrine".
"That is desecration of a very holy place. It hurts me. And it hurts the staff," one cleric told The Sunday Times.
However the staff have stopped short of directly blaming the anti-capitalist Occupy London protests camping on the cathedral's doorstep, and say they are working with the protesters to solve the problem.
They said that onlookers or other people not connected to the protest may have been responsible.
Cathedral spokesman, The Rev Rob Marshall, told the Sunday Times: "We are aware of these kind of problems and raising them in our daily talks with camp members who we are not presuming at all are responsible."
The reports came as Labour leader Ed Miliband backed the protests in an editorial in The Observer.
"The challenge is that they reflect a crisis of concern for millions of people about the biggest issue of our time: the gap between their values and the way our country is run," Miliband said.
Responding for the government, Chief Secretary to the Treasury Danny Alexander said that the protesters were drawing attention to important issues.