THE president of the New York Stock Exchange has pulled out of giving evidence at a Senate hearing into why the Big Board cancelled the stock market listing of Huntingdon Life Sciences, the animal research group, last month.

Catherine Kinney had been scheduled to appear before the US Senate Environment and Public Works Committee into animal rights activism today, but has been replaced by Richard Bernard, the NYSE’s chief lawyer. A spokesman for the NYSE declined to comment about the change of plan.

Ms Kinney’s appearance was considered crucial by the committee as it is understood that it was her decision to stop the listing of Huntingdon’s shares. She had been due to give evidence along with Jerry Vlasak, an animal rights activist banned from Britain for advocating violence against company directors.

The committee wants to know about the connection between Dr Vlasak, a heart surgeon and official spokesman for the Animal Liberation Front in America, and Stop Huntingdon Animal Cruelty (Shac), a group of animal rights protesters who have targeted the research company in a relentless campaign of intimidation, vandalism and violence.

The panel will ask Dr Vlasak if he knows of any threats that would have led the NYSE to cancel Huntingdon’s listing at the last minute. It is understood that the committee will focus its questioning of Dr Vlasak on an attack by animal rights activists this year on a New York area yacht club. Some members of the club are understood to have a close association with the NYSE and Huntingdon’s Wall Street advisers, sources said.

Dr Vlasak told The Times last night, however, that he was not aware of any reason why Huntingdon’s float was pulled, but did admit that he knew about the yacht club attack.

The NYSE has not explained why it halted the listing — a move that angered Huntingdon directors, who were gathered at the NYSE for a celebratory breakfast when the decision to stop their listing was announced by Ms Kinney.

Mr Bernard is set to be questioned just as intensely as Dr Vlasak. The senators are understood to be incensed that the supposed bastion of market freedom in America would apparently capitulate before a threat from extremists.

Last year Dr Vlasak was banned from entering Britain under orders from David Blunkett, the former Home Secretary, because he advocates violence. Dr Vlasak told The Times that he still believes the animal rights movement should use violence. “I think like any struggle against oppression there unfortunately may be the need for violence. Not against innocent people, but against those who are responsible,” he said.