"The (animal rights groups) have had it all their own way. They have intimidated people, but the time has come to speak up and risk it. Who knows what the risk is?" he told the Guardian newspaper.

Stein and his colleague, consultant neurosurgeon Professor Tipu Aziz, could be putting themselves at considerable danger.

Britain's largest and oldest animal testing centre, in Huntingdon, nearly collapsed in 2001 when frequent violent protests caused financiers to pull out.

Plans to build a laboratory to carry out tests on monkeys at Cambridge University were scrapped in 2004 over spiralling security costs.

Animal rights activists have also threatened violence against anyone involved with an animal research centre being built in Oxford, which Stein and Aziz are supporting.

Their stand was strongly welcomed by the Association of the British Pharmaceutical Industry (ABPI), a strong critic of the militants' scare tactics.

The two professors will address a march in Oxford on Saturday to speak out in favour of the new laboratory. Protesters will also march through the town on Saturday and police say they hope to keep the two sides apart.

Building work on the 20 million pound ($35 million) centre was previously stopped for 16 months in the face of persistent campaigns by animal rights group SPEAK. Construction eventually resumed late last year.

"The ALF (Animal Liberation Front) are actively now saying that anyone in Oxford is a target," Aziz told the Guardian.

"What we are seeing in Britain today is a minority dictating how the majority of this country live and that is as undemocratic a process as can be imagined."

FIRE-BOMBING

Britain is home to some of the world's most vociferous animal activists and one security expert told Reuters US authorities regarded the UK as "the Afghanistan of animal extremism".

The government was forced last year to introduce tougher legislation to target protesters who obstruct experiments and threaten medical research.

Scientists, pharmaceutical companies and contract research laboratories have been the target of protests like hate mail, hoax bombs and even the fire-bombing of scientists' cars.

Thames Valley Police said the majority of protests at Oxford were peaceful but that 10 people have been arrested since the start of the year.

Dominic Armstrong of security firm Aegis Defence Services told Reuters this week they predicted animal rights extremism would deepen in Britain and would be increasingly exported across Europe.

However the police unit that deals with the crime, the National Extremism Tactical Coordination Unit, said although there was significant activity in the country, police efforts were starting to bear fruit.