Charles Clarke, the home secretary, has used the government's crackdown on preachers of hate to ban an American professor who speaks for the Animal Liberation Front.

Steven Best, professor of philosophy at the University of Texas at El Paso, had intended to travel to the UK to take part in an event to celebrate the closure of a farm breeding guinea pigs for research.

The closure of the Newchurch Farm business following years of harassment and intimidation, including the theft of a grandmother's ashes from the local cemetery, was widely condemned by scientists and politicians last week.

In the wake of the London bombings of July 7, the Home Office announced it would not allow people to enter the UK who "foment, justify or glorify terrorist violence in furtherance of particular beliefs; seek to provoke others to terrorist acts; [or] foment other serious criminal activity or seek to provoke others to serious criminal acts."

In July Dr Best spoke at an international animal rights conference in England. At that conference, he was quoted by the Daily Telegraph as saying: "We are not terrorists, but we are a threat. We are a threat both economically and philosophically. Our power is not in the right to vote but the power to stop production. We will break the law and destroy property until we win."

According to the newspaper, he added that activists did not want to "reform" vivisectionists but to "wipe them off the face of the earth". The Home Office cited these words in a letter to Dr Best last week banning him from entering the UK. Dr Best, who claims his words have been taken out of context, said he was not surprised by the ban. "It was only a matter of time, especially after July 7. The climate in Britain is totally unbelievable. It's very fascist. It's becoming a police state," he told the Chronicle of Higher Education.