A 'Don't Censor Me' demonstration has been held in Blackfriars Road to coincide with the Stop Porn Culture conference.
The conference held at Wedge House on Saturday opened in the morning without protest but a rally called for the afternoon filled the wide pavement outside the building on the corner of Colombo Street.
An address by sociologist and anti-porn campaigner Dr Gail Dines was called 'The Porning of Culture and the Culture of Porn'.
"Pornography is misogynistic in its production and consumption," said Stop Porn Culture International.
"The goal of this anti-porn conference is to explore how to build materials and programmes to combat porn. We are coming together to develop a broad coalition of feminist organisations to organise together against the sex industry."
Other conference speakers included feminists from Norway, Iceland and Sweden.
The conference organisers had insisted that the event was not the occasion for a debate with opponents.
But during the demonstration both Gail Dines and Guardian columnist Julie Bindel suddenly appeared with plates of biscuits and entered into lively and sometimes heated debate.
Around 50 protesters waving placards included members of the English Collective of Prostitutes and strippers.
The rally was later addressed by Jerry Barnett of pro-pornography group Sex and Censorship who criticised Gail Dines' book Pornland: How Porn Has Hijacked Our Sexuality.
Former porn star Renee Richards who is seven months pregnant said: "Dines and the other so-called feminists at this conference claim all porn has harmful effects. Yet Dines has never stepped on a porn set."