What Exactly is Criminal Law?

Going through criminal proceedings can be a daunting experience, especially if it’s for the first time. This introduction to criminal law should give you some idea of the main principles and procedures, so that when you go to court the whole thing is less mystifying.

Red books and scale of justice

Introduction to Criminal Law - What Exactly is Criminal Law?

Criminal Law is law which involves the state (or The Crown, sometimes referred to as Regina) bringing a prosecution against an individual. Only crimes (or offences) which already exist in law can be used to prosecute people. These are laid down by Parliamentary Law (statutes like the Theft Act 1968, or by previous decided case history in the courts (common law).

Innocent until proven Guilty?

One of the first principles that need to be covered in any introduction to criminal law To convicted someone of an offence, the Prosecution has to show the court that the person has committed the offence to a level of certainty which is very high. The phrase that judges use is you must be satisfied so that you are sure. Verdicts along the lines of he probably did it, or if she didn't do it, who else did?, are not usually enough for a conviction. The prosecution must show beyond reasonable doubt that the offence occurred and was done by the accused person (or the defendant_). In the eyes of the Criminal Courts, not sure is not guilty.

Juries and Judges

In the criminal courts, there are generally two levels of court. The first level is the Magistrates Court. This court deals with less serious types of offence, such as most motoring offences, or low value thefts and less serious assaults. However, this court can still impose prison sentences.

In the Magistrates Court, questions of law (procedure and legal issues) are dealt with by part time judges called Magistrates, or by a District Judge, who is a former lawyer. Magistrates are people from the community who become judges on a voluntary basis after being given their own introduction to criminal law in the form of basic legal training. They are helped by the Court Clerk, who is a qualified lawyer, whose job it is to make sure they get the law right. The District Judge is a qualified, paid judge. He can appear as a judge on his own, but the magistrates (sometimes called Lay Magistrates or a Lay Bench) must appear with two or three in court at any one time.

In the Magistrates Court, there are no Juries. The Lay Magistrates or the District Judge decide not only on the law, but also whether someone is guilty or not guilty. This means that for some less serious offences, there is no right to trial by jury, which comes as a shock to some people, as Trial by Jury has in the past been considered by most people to be a constitutional right.

In the Crown Court, a jury will be first told that they have to find the defendant guilty or not guilty by unanimous vote. A majority of 9 to 3 is not enough. If the jury cannot come to a unanimous verdict, a judge might tell them that a majority verdict will do, this being 10 of the 12 members of the jury in agreement. If no verdict can still be reached, a re-trial may be ordered.

What the Prosecution must prove

The prosecution must prove two things before a person can be convicted of an offence. They must prove that the person did something illegal, and that he meant it. They must prove that the person committed the offence. Secondly they have to prove that the person knew it was wrong, or that he knew he was doing it. To simplify, they must prove that the accused did it, and did it on purpose.That is a basic explanation which in a brief introduction to criminal law is fairly straightforward, but it is actually a fairly complex area of law, explained using the latin phrases actus reus (guilty act) and mens rea (guilty mind). Most clients will not want or need to worry about this fairly confusing language, beyond the earlier explanation at the beginning of this paragraph.


Just because someone is guilty of committing an illegal act, and of meaning it/knowing it was wrong, that doesn't definitely mean that they are guilty of the offence. They might have a defence, or a good reason why they should not be convicted.

My wife made me do it, or I really needed the money aren't usually regarded as reasons adequate for a defence. But if someone committed an offence while, for example, sleepwalking or protecting themselves or their family, then that could be a defence which would help them avoid being found guilty.

Introduction to Criminal Law on Self Defence / Defence of Someone Else / Defence of Property etc.

If someone commits an offence of violence (such as assault) to prevent getting injured, to prevent someone else getting injured, or to protect his or her property, then that can sometimes mean they are entitled to a defence. The force used must be necessary, and reasonable. That means there must be no other obvious course of action to avoid the injury or damage (such as running away), and the level of force used must be proportionate to the threat so stabbing someone to stop them scratching your car probably would not count as a defence in law, and the fact that the defendant thought the action was reasonable is not enough to suggest that it was. However, the jury have to accept the facts as the defendant honestly believed them to be at the time, even if he or she was mistaken. So if the jury believe that a defendant honestly thought that his attacker had a knife and so attacked him, the jury have to take that belief into account, even if he was only holding a broom handle. Then they can consider whether his reaction, for example stabbing the attacker first, was reasonable by their standard.

Several other defences to charges of use of force have been added over the years by Parliament. They include:

  • The Prevention of a crime in progress

  • Citizen's / Police arrest

  • Duress

Brief Summary / Introduction to Criminal Law Regarding Mental Defences

There are other defences which relate to the mental state of the person who is accused. They include:


This is a defence when the act has been done unconsciously and involuntarily, €œdone by the muscles without any control by the mind. An example could be sleepwalking, or being in a trance, or even hypo/hyperglycaemia caused by diabetes. There must be a total loss of control of the body and it cannot be self-induced, so alcohol related blackouts don't count.

Diminished Responsibility

This is a partial defence to murder only. It can reduce murder to manslaughter. The Law says that the defendant must prove that he was suffering from an ‘abnormality of mind' caused by something inherent and which substantially impaired the defendant's responsibility for the killing. It does not have to be the only cause provided it still substantially impaired the mental responsibility of the defendant. Therefore consumption of alcohol, for example, can go alongside using diminished responsibility as a defence.


This is another partial defence to murder, but is not a defence to any other offences. There are two stages to the test for provocation:

  • The first is that the defendant

    must have been provoked

    and lost his self control. This depends on the evidence and what the jury decides

  • The second stage is to decide

    whether the provocation was enough

    to make a reasonable man react in that way

The law says that only the age and sex of the defendant can be taken into account for the second test, so being particularly high strung or sensitive is not to be considered.

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