Protesters forced the Oxford Union to briefly delay a controversial free-speech debate tonight that featured the British historian David Irving, who served a prison sentence in Austria on charges of denying the Holocaust, and the leader of Britain’s far-right British National Party, Nick Griffin.

According to reports from the Associated Press and BBC News, 20 to 30 demonstrators pushed their way into the debating chamber to protest the inclusion of the two men, forcing the event to begin more than an hour after its scheduled 8:30 p.m. start.

Hundreds of demonstrators had gathered in the City of Oxford before the debate, The Guardian reported, and many students with tickets to the controversial event were blocked from entering the building by chanting protesters.

There had been speculation that Mr. Irving would pull out of the debate, but hours before it took place he told The Guardian that he would go ahead. “I thought the traditional enemies would have been doing enough to silence me at Oxford,” he said. “But I have the balls — you’ll see what I mean.” Mr. Irving arrived at the debate carrying a ball and chain.

The University of Oxford was at pains today to distance itself from the event. A statement posted on the university’s Web site emphasized that the union “is an independent debating society” and that “the university does not have jurisdiction over its events.” —Aisha Labi