Police have dropped an investigation into comments made by controversial former US Marine Ken O'Keefe at an Israel Apartheid Week event.
Officers studied video footage of Mr O'Keefe telling an audience that Israel "must be destroyed" and comparing Jews to Nazis, but concluded that no criminal offence had been committed.
Mr O'Keefe had responded to news of the investigation by tweeting: "Bring it ****ing on."
During the debate at Middlesex University's Hendon campus last month he claimed Mossad was "directly involved" in the September 11 terror attacks on the United States.
There were heated scenes as Mr O'Keefe clashed with supporters of Israel following his comments. He was later reported to the police by two audience members who believed he had incited racial hatred.
A Barnet Police spokesman confirmed: "The comments made were in an open debate and listeners were encouraged to agree or disagree with what was said.
"Officers have gone through the video clips and media material and have agreed that there are no criminal offences."
The JC understands the decision was taken by officers from the force and the file was not passed to the Crown Prosecution Service for review.
One leading criminal lawyer who studied footage of the meeting said he believed police could have brought a charge against Mr O'Keefe and tested the law in court.
He said comments that victims felt amounted to incitement to racial hatred regularly fell into a "grey area" between the public interest in pursuing a prosecution, and the right to free speech.
But the lawyer added: "The police view is often 'forget it, we'll not get involved, it's just politics between Jews and extremists. We'll say no crime has been committed'."
He warned that prosecutions could "make martyrs" of those charged and might lead to lengthy criminal hearings, with inevitable appeals processes meaning cases could each drag on for more than a year.