Direct action against another's property: is it ever justifiable? In the wake of the Prague protests, we ask if it can be right to break the law as part of a protest

Yes - Bruce Kent: 'It should be self-evident that those who own land have no right to do what they like with it'No - Ann Mallalieu: 'Peaceful demonstration within the law is far more effective than trashing a field of maize'

Bruce Kent There are forms of direct action of which most respectable people disapprove instinctively: the actions of those who destroy GM crops, or who damage bits of nuclear submarines, or who try to stop IMF meetings. Can they be justified? Here, I have to declare an interest. It is some years now since I stood in the dock accused of an intention (freely admitted) to commit criminal damage. I had been arrested while carrying wire cutters, about to cut the wire protecting the US nuclear base at Sculthorpe.

Bruce Kent There are forms of direct action of which most respectable people disapprove instinctively: the actions of those who destroy GM crops, or who damage bits of nuclear submarines, or who try to stop IMF meetings. Can they be justified? Here, I have to declare an interest. It is some years now since I stood in the dock accused of an intention (freely admitted) to commit criminal damage. I had been arrested while carrying wire cutters, about to cut the wire protecting the US nuclear base at Sculthorpe.

I believed - and continue to believe - that in international law the use and threatened use of nuclear weapons is illegal, and I wanted to obstruct the commission of a crime. The judge told the jury that it was for him to decide on the law, and that international law was irrelevant. Their job was only to consider the physical facts - and I was duly convicted.

Those who destroyed GM crops argued from a similar basis, the jury were allowed to hear their arguments, and they were convinced by them. It should be self-evident that those who possess land do not have a right to do what they like with it.

Ann Mallalieu Lord Melchett and his protesters successfully used the defence of necessity. Having admitted damaging crops they maintained that their actions were necessary to prevent greater harm, and the jury who acquitted them apparently agreed. But protesters cannot rely on the law to afford them a defence of necessity if they damage other people's property. The test which the court applies is an objective one; that the defendant believes that what he did was necessary to avoid the end is not enough. Lord Melchett was lucky with his tribunal.

BK I am no believer in the sanctity of private property, or the absolute authority of law. St Thomas Aquinas said that "human law is law only by virtue of its accordance with right reason ... Insofar as it deviates from right reason it is called an unjust law. In such a case it is no law at all, but rather a species of violence."

AM I do not believe that it is right, whatever the provocation, to break the law. The television scenes of rioting from Prague by anti-capitalist protesters, with serious violence, tear gas, riot gear and blood show where that course of action can lead. The May Day disorder in London cost the police £2m. I doubt if those responsible gained any new support and almost certainly wiped out any potential sympathy for the cause they claim to champion.

It was not the poll tax riots which changed government policy but the non co-operation of taxpayers in such numbers that enforcement became impossible for the authorities.

BK Do I support violence of the kind, perpetrated by a minority, which we saw in Prague? Certainly not. There can be no justification for injuring other people in the pursuit of any cause, however just.

There are occasions when people have the moral right to damage property if they believe that in so doing they are helping to prevent a crime or other moral outrage from being committed. Such people must be willing to take the penal consequences of their actions, and they invariably are.

Law stands between us and the jungle. It commands respect and obedience up to the point when serious, considered conscience says this cannot be right, and is driven to take action against property whatever the consquences.

AM How far should protest properly go? At the Labour Party conference the Country- side Alliance staged a demonstration opposite the confer- ence centre every lunchtime. We waved banners, listened to speeches, sang, cheered and laughed. The mounted police- men were soon cheering the speakers, too. They were four days of good humour and impeccable behaviour, without any violence or damage. Yet John Prescott used his main conference speech to vilify the demonstrators whom, he said, had "contorted faces" and had made him "redouble his determination" to ban hunting.

When lawful and peaceful protest is dismissed so offensively by someone in a position of power the frustration and anger generated becomes difficult to contain, but it must be.

A government can only govern with the consent and co-operation of the people. Peaceful demonstrations within the law, backed by public sympathy, and well organised and disciplined direct action, is far more effective in the long term than trashing a field of maize.

Bruce Kent is the former chairman of the Campaign for Nuclear Disarmament. Baroness Mallalieu is a Labour life peer and president of the Countryside Alliance.