He said: “Rumour had spread there might be a protest outside an immigration centre of Hoe Street during this event.
“Mr Jones made a speech that was amplified through a public address system to the crowd.
“During this speech Mr Jones referred to the other side, if you like, as disgusting Nazi fascists, and he said that their throats needed to be slit and as he said that he drew his finger along his throat.
“This is, the prosecution say, in a setting where violence could readily have been anticipated.”
Mr Holt said Mr Jones was “rabble rousing” a crowd which has been described as “tens of thousands” in size.
He said the video clip “went viral and came to the attention of the police and others and led to Mr Jones being arrested on the following day”.
Mr Jones was also suspended by the Labour Party.