Polygraph tests, also commonly known as “lie detector” tests, are often used as a tool to assess the likelihood that an individual is lying or being deliberately misleading about a specific event or fact. However, the question that often arises is whether such tests can be used as admissible evidence in court or during other legal proceedings. In this article, we will explore the use and admissibility of polygraph tests in the UK legal system.

What is a Polygraph Test?

A polygraph test is a process in which a subject is asked a series of questions while being monitored for changes in breathing patterns, heart rate, and perspiration levels. This is done using a combination of sensors attached to the chest, arms, and fingers. The resulting data is interpreted using a sophisticated algorithm that can predict the likelihood of the subject having answered the questions truthfully.

Reliability of Polygraph Tests

The reliability of polygraph tests is a subject of much debate. While some studies suggest that they are around 80-95% reliable, depending on the type of test, the number of questions asked, and various other factors, others argue that they are not reliable at all. People often ask whether it is possible to cheat on a lie detector test. While it is possible for an individual to consciously control their breathing and heart rate for a short time, it is extremely hard to maintain this control, and virtually impossible to prevent the tiny changes in perspiration that are produced as a result of the “fight or flight” response of the nervous system.

Admissibility of Polygraph Tests in Court

Lie detector tests are not routinely used in courts in England and Wales. However, they can be used in some circumstances, depending on the type of court. In civil courts and tribunals, polygraph tests are not used as evidence in their own right but can sometimes be used to add weight to the evidence of either party. In the criminal courts, lie detector tests are not allowed as evidence, supporting or otherwise.

It is usually up to those presiding over the court on the day as to what types of evidence are allowed. While polygraph tests can be a useful supplement to existing evidence, there is no guarantee that they will be accepted for use in any individual trial.

Other Legal Uses for Polygraph Tests

Aside from their use in court cases, lie detector tests can also be used as a tool in evaluating the potential for release of existing offenders from prison. In the UK, polygraph tests are used by the National Offender Management Service to inform decisions about the early release and licensing conditions of convicted sex offenders. Individuals are tested every 3-6 months, and the results of the tests taken into consideration along with other evidence. The success or failure of a lie detector test does not guarantee a particular parole decision, and individuals have a right to appeal a license revocation that has occurred as a result of evidence from a polygraph test.

A similar system has recently been proposed by the government for those convicted of domestic abuse, whereby offenders would be subject to polygraph testing as a condition of their license following their release from custody.

Finally, the police in some countries use lie detector tests for investigative purposes, for example, to rule out suspects from their inquiries, obtain a confession, or to generate more lines of inquiry. While this does not currently happen in the UK, there are calls for this approach to be adopted here in the future.


Polygraph tests have their limitations, and their admissibility in court and other legal proceedings is limited in the UK. However, they can be used as a tool to supplement existing evidence in some cases, such as in evaluating the potential for the release of offenders from prison. It is important to remember that the use of polygraph tests is heavily dependent on the context in which they are being used, and their reliability is still a subject of much debate.

As technology advances, the accuracy of polygraph tests may improve, and it is possible that their use in legal proceedings may become more widespread. However, for now, it is important to be aware of the limitations of polygraph tests and the circumstances in which they can be used in the UK legal system.