In regard to criminal law, the substance of the law is much the same throughout the common-law countries. In both the United Kingdom and the United States, the 20th century was a period during which it was thought that undesirable behaviour could be eliminated by rigorous law enforcement. In the early part of the century, this led to the criminalization of much personal behaviour—including some sexual practices, gambling, and the use of alcohol and drugs—that was previously beyond the reach of the law, the most noteworthy example being the prohibition of alcoholic beverages in the United States from 1919 to 1933. At the beginning of the 21st century, some such behaviours were being treated as medical or psychological problems rather than as criminal ones.

The death penalty, which had been slowly removed in most U.S. states since the end of the 19th century, was revived during the 1970s after the Supreme Court ruled its use constitutional. Capital punishment was eliminated in the United Kingdom in 1965.

More important differences appear in the rules of criminal procedure. In England, this rests on modern legislation. Accused persons may now testify at the trial or not, as they wish; they are entitled to legal counsel; and they are assisted out of public funds when they are accused of serious crimes and are unable to afford to pay the costs themselves.

Canada has a Dominion Criminal Code, which covers major crimes. It also has a Canadian Bill of Rights and provincial laws, such as the Ontario Human Rights Code. India has an overriding Bill of Rights.

In the United States criminal procedure has become a constitutional matter, with a kind of federal common law of criminal procedure overriding state law in many instances. Thus, due process of law under the Fourteenth Amendment to the federal Constitution and the Federal Rules of Criminal Procedure confer protection on accused persons.

English courts are reluctant to admit recordings of private conversations unless supported by direct evidence of persons present, and this is generally the position taken in the United States, although emergency wiretapping and other electronic monitoring are permitted with the permission of a court or in some cases involving national security. The USA PATRIOT Act (2001) and subsequent reauthorizations significantly expanded the search and surveillance powers of law-enforcement agencies in the United States to include limited monitoring of telephone and electronic communications without probable cause (a showing of facts that would lead a reasonable person to believe that the surveillance would likely uncover evidence of criminal activity). English and U.S. law generally exclude confessions unless they are made freely and spontaneously. If evidence is found by unlawful means—such as by searching a house without a warrant—English law permits such evidence to be used, but U.S. law generally does not, though significant exceptions were created by the Supreme Court from the late 20th century. The main difference between English and U.S. safeguards is that English protections rest on statute or case law and may be changed by ordinary statute, whereas U.S. safeguards are constitutional and cannot be relaxed unless the Supreme Court later reverses its interpretation or the Constitution is amended.

The future of the common law

In the past, the law performed the function of a referee in a free economy and was called in to apply generally accepted ideas of right and wrong to individual disputes. Today, law often forms an instrument of governmental policy or results from social pressures on the government. Law, therefore, is increasingly administrative.

Another tendency, and one that is likely to be reinforced, is an increasing reliance on statute law and codification as instruments of legal development. At one time the English Law Commission considered drafting a contract code, and the law of tort has been the subject of several statutes. When the United Kingdom entered the European Economic Community, it was thought that there might be pressures to make English law more accessible by codifying it along the lines of the continental model. Harmonization of the laws of the member states, however, did not require this, and Britain’s withdrawal from the EU in 2020 made the point moot. The introduction of human rights as a basic element in the domestic law of the United Kingdom has brought about change, as has the growth of international tribunals. In the United States the legal sovereignty of the states impedes such a radical change, but uniform state laws are becoming more common.

In view of the general tendency in modern society of shielding the individual as fully as possible from the consequences of chance accidents, the judge-made law of tort may eventually be replaced, as it was for a time in New Zealand, by a comprehensive system of official or private insurance similar to the present compulsory third-party risk insurance available for motor vehicles. The New Zealand experience, however, suggests that this is an expensive alternative. Public law is also gaining on private law in other fields—in real-property development, for example, public zoning or urban planning rules are already more important than the traditional restrictions imposed by individual neighbouring landowners. Public-welfare laws on child care and adoption, pensions, and social security are often more important than the older private law based on the rights of spouses and children.

English and American law can still be recognized as partners sharing a common root in the common law before the 18th century. But they are increasingly diverging, and English law, with or without the European Union, now shows much more specific similarities to the law in other countries of continental Europe than would hitherto have been admitted.