A top adviser to Britain's two most powerful animal rights protest groups caused outrage last night by claiming that the assassination of scientists working in biomedical research would save millions of animals' lives.

To the fury of groups working with animals, Jerry Vlasak, a trauma surgeon and prominent figure in the anti-vivisection movement, told The Observer: 'I think violence is part of the struggle against oppression. If something bad happens to these people [animal researchers], it will discourage others. It is inevitable that violence will be used in the struggle and that it will be effective.'

Vlasak, who likens animal experimentation to the Nazis' treatment of the Jews, said he stood by his claim that: 'I don't think you'd have to kill too many [researchers]. I think for five lives, 10 lives, 15 human lives, we could save a million, 2 million, 10 million non-human lives.

Stop Huntingdon Animal Cruelty (Shac), which campaigns for the closure of Huntingdon Life Sciences, has close links with Vlasak. He has also advised Speak, the organisation that last week forced out the contractor building an £18 million primate research laboratory in Oxford.

David Martosko, research director at the Centre for Consumer Freedom, which monitors activist groups on behalf of business interests, responded by saying Vlasak was 'one of the most dangerous animal rights zealots on the planet'. He added: 'He's not making bombs, but he is making bombers.'

Vlasak will address an animal rights conference organised by Shac and Speak in September. Legal experts warned that, if he uses his speech to promote violence, he could be charged with incitement.

Vlasak has made a series of incendiary claims that will alarm moderates in the animal rights movement and reinforce claims that Shac and Speak are fronts for extremists.

Three months ago, he told a US television audience that violence was a 'morally justifiable solution'. Earlier this month, he gave a speech in Virginia in which he said: 'It won't ruin our movement if someone gets killed in an animal rights action. It's going to happen sooner or later.'

Vlasak meets Shac leaders regularly. He has played a big part in writing speeches, directing its strategy and advancing scientific arguments against animal experimentation. He also worked with Speak in its successful effort to prevent the building of a primate research centre in Cambridge and says he plans to work with the group on its Oxford campaign.

Other animal rights groups have distanced themselves from him. Until recently he was a member of the Physicians Committee for Responsible Medicine (PCRM), a group funded by the powerful lobbying group People for the Ethical Treatment of Animals (Peta) and endorsed by Shac.

But a PCRM spokeswoman told The Observer: 'He is not a member of the organisation.' Vlasak confirmed he was not working with the PCRM 'at the moment'.

While acknowledging that his views might alienate some people, Vlasak, who claims animal experimentation 'wastes billions of pounds a year', said more and more people in the animal rights movement were drawn to violent action. 'The grass roots are tired of writing letters. The polite approach has not worked,' he said.

Patricia Hewitt, the Trade and Industry Secretary, last night promised that the law would be strengthened to tackle the growing number of incidents. On Friday Home Office Minister Caroline Flint will unveil measures designed to clamp down on protesters. It is believed ministers are frustrated that the CPS and the police have not taken a sufficiently robust stance against the movement.

One of the City's largest institutions, the National Association of Pension Funds, is about to offer a £25m reward to help catch protesters who threaten businesses associated with animal research firms.

Yesterday, 300 Speak activists celebrated their coup in forcing building firm Montpellier to pull out of the new Oxford primate research centre with a march through the city centre. Protester Robert Cogswell attacked the NAPF's offer of a reward. 'It should stop wasting money and start looking at why people are taking illegal action,' he said.

Yesterday Natasha Avery, a spokeswoman for Shac, declined to comment on its links with Vlasak. Speak did not return calls.