Mr Horne is fasting in protest at the Labour Government's failure to set up a Royal Commission to examine the issue of experiments on animals. It is true that the Labour Party has broken the spirit of its pre-election promise. In 1996, Tony Blair put his name to a document called "New Labour, New Life for Animals" which said: "We will support a Royal Commission to review the effectiveness and justification of animal experiments and to examine alternatives." This pledge was not repeated in the manifesto, but it was referred to obliquely: "We have advocated new measures to promote animal welfare," the manifesto declared.
Now, however, ministers say a Royal Commission would be too expensive and might delay action. It is an argument that would carry more weight if there were any action to delay: so far the Government has managed to end the testing of cosmetics on animals, which accounted for just 250 rabbits, guinea pigs and rats out of a total of 2.7 million animals a year. And, while it is true that Royal Commissions are cumbersome - they "take minutes and waste years", as Harold Wilson said - no other way of assessing the need for animal experiments has been set up.
This is regrettable, less from the point of view of cruelty to animals than because it provides a grievance against which extreme measures can be mobilised. If the Prime Minister had announced a review, it would have been a chance to educate the public about the balance that has to be made between the welfare of humans and that of other animals. As it is, the cry of "betrayal" provides moral fuel for the arsonists, saboteurs and hunger strikers of the animal rights movement, while giving them little incentive to consider the detail of complex public policy.
And fanaticism is a dangerous thing. Absolutism in pursuit of rights which are not absolute, such as those of animals, can never be justified.
It leads to the kind of illogic which ends up with the release of mink to slaughter wildlife and to die painful deaths or with the argument that the lives of scientists who use animals to alleviate human suffering are less important than those of mice. The responsible wing of the animal rights movement must ensure that the tragedy of Mr Horne does not become a greater one.