The animal rights lobby in Britain has crafted a popular image of itself as a movement dedicated to protecting fluffy white rabbits and mice from power-crazy scientists intent on carving them up to test the colour of lipstick.

The animal rights protectors hold their placards outside Downing Street and the Home Office, but sometimes the more militant members send incendiary devices to stores selling fur coats. And now, a lone maverick, Barry Horne, has been on hunger strike for almost two months and is said to be clinging to life by a thread.

For Horne (46), who is on his third hunger strike in protest against vivisection, the prognosis is not good. He was moved to York District Hospital earlier this week from Full Sutton Prison, where he was serving an 18year sentence for arson, after prison officials became concerned about the state of his health.

Today is his 60th day on hunger strike and, according to his supporters, he has lost the sight of one eye, his liver is failing and he has lost 40 per cent of his body weight. The prison service has said Horne's condition is "serious, but stable", and the police are drawing up an action plan in anticipation of an escalation of protests if he dies.

Horne began his hunger strike with a list of six demands, including an end to the issuing of all vivisection licences and a total ban on all vivisection carried out for non-medical purposes.

In recent contacts with the Home Office, he says he conceded all of his demands because he was led to believe the British government would carry out its election pledge to establish a Royal Commission to investigate the whole area of animal testing. The Labour Party says this election pledge does not exist but was flagged in a pre-election pamphlet, which was then superseded by a woolly paragraph in the manifesto promising to "advocate new measures to promote animal welfare".

Labour points out that far from breaking its manifesto pledge, cosmetic testing on animals has recently been outlawed and the Royal Commission has not been ruled out: it's just a question of finding the time and the money. Horne says he can't wait any longer.

In a twist of the "dirty war" of animal rights, where economic sabotage and peaceful protest sit uncomfortably side by side, this week a group calling itself the Animal Rights Militia threatened to kill 10 people on a hit list if Horne dies. The group, which was formed in 1984, claims that the mainstream animal rights group, the Animal Liberation Front, does not go far enough in its opposition to vivisection.

ARM favours direct action - it claims that in 1984 it tricked Mars Confectionery into believing it had poisoned Mars bars because it believed the company was performing "horrific" tooth decay experiments on animals. It also claims to have sent incendiary devices to stores selling leather but some animal rights activists are dubious, not only about the threats and the firebombs, but about ARM's existence.

"Some people, our rivals, are trying to discredit us by linking us with extreme groups," says one animal rights activist who does not believe in violence. "Anyone can send a threatening fax, and no one can get in touch with them so it doesn't prove they exist."

The militant wing of the animal rights lobby has also been blamed for the recent attack on a mink farm, which led to hundreds of mink being released to roam around the countryside. They have sabotaged research laboratories on a fairly regular basis and in an unfortunate incident two years ago one of their number died during a protest against live animal exports.

Meanwhile, Barry Horne remains on hunger strike willing to die for his beliefs. He has written a "living will", insisting he should not be force-fed if he slips into a coma. He could be dead within hours if his supporters agree to his request.

"We don't want him to die . . . that is totally his decision," says John Pounder of the Animals Betrayed Coalition group. The deadlock seems immovable and the Home Office is adamant that it will not bow to blackmail, but for Barry Horne time is quickly running out.