Alan Macfarlane considers what makes law effective. Is it down to demographics, isolation, independence from politics or a belief in the right to life, liberty and the pursuit of happiness?

In most societies, people fear and hate the law, or believe it is weak and corrupt. To persuade people to use it as the normal process of settling disputes is enormously difficult and requires immense political skill and good fortune. It happened early in England, but it is still not widespread in many parts of the world. Looking at whether people are prepared to settle disputes through legal processes - the "rule of law" - rather than by force could be one way to index a law or laws as effective.

The "rule of law" could also be taken to mean that all actions and all power are ultimately under the law - that above those who rule there is something higher. Most legal systems develop differently. At first, the rulers may say: "We make the laws and we keep the laws." But after a time, they forget the second half and begin to see themselves as above the law. You can see this in Stalin's Russia, Chairman Mao's China or France in the late 17th century - where there was one law for the powerful and rich and another law for everyone else.

The "rule of law" depends on the uniform application of laws and a common procedure. It means that the legal process should be separated from the political process, that judges and courts should be independent. All of this is difficult to sustain. Powerful forces - economic and political - are constantly pushing to bias the law in their direction. These separations are particularly fragile in times of war, whether during real wars - such as the Second World War - or during invented or ideological wars, such as the "wars" against medieval heretics, "wars" against Satan and his witches, "wars" against communism in the McCarthy purges of the 1950s, and "wars" against terrorism. In each case, civil liberties are eroded and legal independence crushed. We saw this all too clearly in the US and Britain as fear was used to justify suspension of legal rights after the terrorist attacks on the World Trade Center in 2001.

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A second index of effectiveness concerns the degree to which people abide by legal decisions. The problem is to persuade people to accept a legal process that takes them out of their ordinary lives, where they may have become entangled in relationships of conflict, and puts them in an arena that is unfamiliar before rearranging their lives. It takes pressure to persuade people to accept a decision they may think is against their interests. To force acceptance, the law can be a dramatic, elaborate process. People dress up in strange costumes, the judge sits high up above the court, long words are used in a strangely formal way. There are often dramatic public punishments, as in the so-called "theatre of Tyburn" where criminals were taken through the streets and executed before the crowds in 18th-century England.

A third sense of effectiveness concerns the degree to which citizens feel protected by their laws. In almost all serious legal cases, you have a confrontation between state and citizen. The state has almost all the power and the single individual is inherently weak. So if the state says you are suspected of an offence, how can you defend yourself? This is why the jury system is so effective. Under this system, your equals decide your guilt or innocence. Members of the jury are not themselves on trial but are observers and arbiters. It is one thing to grind down a single individual already accused of an offence. It is entirely different to be able to persuade 12 free individuals, who have been told, on oath, to judge fairly, without fear or favour. The jury acts as a filter to state power, a protection for the single citizen or subject. It is a key institution in any democracy.

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Most countries in Western Europe had juries of a sort 1,000 years ago. The tribes that destroyed the Roman Empire introduced a legal system of trial by peers in front of travelling judges, and this was maintained for half a millennium. Yet almost all had given up the jury system by the 18th century. One reason was social. In the 15th century, jurist Sir John Fortescue noted, when comparing the jury system of England with its absence in France, that juries work only if the countryside is filled with a large class of moderately affluent, educated and independent people who can act as jurymen. England had this class; France did not. Second, most of Europe was recolonised by a form of absolutist Roman law from the 14th to 17th centuries. This was based on an inquisitorial form of justice, where magistrates judged cases without the use of juries. England alone avoided this "reception" of Roman law and maintained its old jury system. However, there are increasing calls for its abolition in some cases, with politicians and reformers citing the delays, expenses and inefficiencies of jury trials. That members of the public will gradually find themselves directly confronted by the state, and no longer protected by their peers, will take time to become obvious.

Magistrates have provided another major protection for the citizen since they are independent of the Government. They ensure that justice is local, that it is decentralised and that ordinary citizens can understand the law.

England would have had a very different history without them. For example, magistrates formed the backbone of the resistance to, and ejecting of, James II in the "Glorious Revolution" of 1688. More generally, their very presence inhibits the pretensions of the executive. Yet, like juries, they are a threatened species as pressures grow to replace them with stipendiary magistrates - paid and trained lawyers who, inevitably, have a closer association with the state.

The degree to which the public trusts the law is deeply affected by its executors, the police. Until the middle of the 19th century, the English police were untrained, ordinary villagers whose duty it was, turn by turn, to act as constable. They wore no special uniform, carried no special weapons, controlled no police station or local prison. They were part of the local community and were not seen as external, armed enforcers of a central power in the way that the police were almost everywhere else in Europe.

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This localised police force made the laws more effective. The police knew their community because they were part of it. Because they were trusted, information came to them. They did not have to be physically present to deter crime or disorder. Martial policing by an "occupying power", without local support, is usually disastrous.

Finally, what makes a law effective is the way in which people feel it runs with their interests and not against them. When it becomes a tool to alter a social structure quickly it can create deep tensions. We can see this in relation to the basic premise of human rights. It is assumed in modern British law that individuals have rights. Men, women, children, disabled people, the unborn foetus and even animals have intrinsic "rights". Few societies in the world share this view. It is usually thought that an individual exists only as part of a group: he or she has rights in relation to others, and these rights are inseparable from responsibilities; there are no intrinsic rights that come with birth. The idea that "life, liberty and the pursuit of happiness" are intrinsic and inextinguishable human rights would be regarded by a large part of the world, even today, as an outrageous claim. When the British imported the idea into India in the 19th century it caused immense confusion. A member of a lower caste, a woman, a child, had never been conceived of as having the same intrinsic rights as a high-caste person, a man, a grown-up.

This assumption of individual human rights is a very old feature of British law. It has now spread over the world and become a central doctrine of a new form of mission activity. It has many merits. The protection of the weak against the strong is attractive. The rebalancing of unequal relationships has benefited from the concept of individual human rights that are protected by the state.

However, taken to extremes, and without counterbalancing rights of communities - or the responsibilities that go with these rights - emphasis on individual human rights can be as dangerous as their absence. It throws the law into disrepute. To many, the obsessive attention to human rights currently being fostered through European legislation is having this effect. Legal systems are on a continuum. At one end are those in which the law is imposed by the central absolutist government to keep a reluctant population in sullen submission. At the other extreme, in many simple societies, people run their own legal system through consensus and self-policing. By chance, and through the advantage of being an island, the British have been able to maintain a position towards the self-enforcing end. This has not only given them a stable, moderately fair and trusted legal system, but has also underpinned their religious and economic freedoms. Overblown fears of terrorism, combined with an overly bureaucratic model of government emanating from the European Union, are in danger of pushing the system rapidly along this continuum towards the absolutist end.

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Alan Macfarlane is professor of anthropological science at Cambridge University.