A hardline American animal rights campaigner who believes there is a "moral justification" for using violence, and even murder, against scientists is to be banned from visiting Britain.
Jerry Vlasak, a Los Angeles heart surgeon and an adviser to various animal rights groups, was to fly to Britain next month for a conference to be held by two anti-vivisection groups, Speak and Stop Huntingdon Animal Cruelty.
However, David Blunkett, the Home Secretary, is determined to keep him out following comments he made last week that the killing of some vivisectionists was justified as it could save millions of animals.
The Home Office said an individual could be barred if he posed a threat to national security or was at risk of committing or inciting acts of violence or promoting racial intolerance that could threaten public order.
Officials have begun preparing an exclusion order of the kind used to exclude Louis Farrakhan, the American leader of the militant Nation of Islam group, since 1986.
Mr Vlasak, 46, was quoted in a newspaper last weekend as saying: "If something bad happens to these people [vivisectionists] it will discourage others. I don't think you'd have to kill too many. I think for five lives, 10 lives, 15 human lives, we could save a million, two million, 10 million non-human lives."
Later, he said he had not been calling for assassinations, but made clear he had no moral objection to the use of violence to fight for animal rights.
A Home Office spokesman said: "The Home Office has sent a warning to a number of US activists that [it is] examining statements they have made about the issues involving potential violence in the UK."
A senior official confirmed: "We will exclude Vlasak."
Last week, the Government announced plans to toughen the law to curb the growing incidence of harassment of animal research projects.