Polygraph Tests and the Law
The truth, the whole truth, and nothing but the truth: Polygraph tests and their role in the legal system
By Regan Peggs of Regan Peggs Solicitors
Are Lie Detector Tests Admissible in Court?
A common question from clients is whether polygraph tests, often referred to as “lie detector tests,” can be used as admissible evidence in court or other legal proceedings. But what exactly are polygraph tests, how reliable are they, and what does the law say about their use?
What Is a Polygraph Test?
A polygraph—or lie detector—is a tool designed to assess whether someone is being truthful or deliberately misleading regarding a specific fact or event. For those interested, you can also hire a private detective to assist with polygraph testing.
During the test, the subject is asked a series of questions while sensors monitor physiological changes such as breathing patterns, heart rate, and perspiration. This data is analyzed using advanced algorithms to estimate the likelihood that the subject’s answers are truthful.
How Reliable Are Polygraph Tests?
Polygraph tests are generally considered to be 80-95% reliable, depending on factors like the type of test, the number of questions asked, and the conditions under which the test is conducted.
Some people wonder if it’s possible to cheat a lie detector test. While it’s true that someone can temporarily control their breathing or heart rate, sustaining this control is extremely difficult. It’s virtually impossible to suppress the subtle perspiration changes triggered by the nervous system’s ‘fight or flight’ response.
Medications can also influence test results—although pre-testing measures, including neutral questions, help establish a baseline for comparison. However, psychoactive substances, including cannabis or alcohol, can significantly skew results and render them invalid. That said, polygraph examiners are trained to identify signs of substance use, and the levels required to disrupt results are usually noticeable even to casual observers.
Polygraph Tests as Evidence in Court
In England and Wales, polygraph tests are not routinely permitted as evidence in court. However, their admissibility depends on the type of court and specific circumstances.
Courts in the UK fall into several categories, including criminal, civil, family courts, and employment tribunals. These are presided over by magistrates or judges (and sometimes juries), who evaluate the evidence presented, assess credibility, and issue rulings based on the law and their judgment.
In civil courts and tribunals, polygraph tests cannot serve as standalone evidence but may occasionally support the claims of one party. In criminal courts, however, polygraph evidence is not admissible under current standards.
Ultimately, it is up to the presiding judge or tribunal to decide what types of evidence are permissible. While polygraph tests can occasionally complement existing evidence, there is no guarantee they will be accepted in any given case.
Other Legal Uses for Polygraph Tests
Beyond courtrooms, polygraph tests have found a role in offender management, particularly in evaluating the suitability of early release or parole conditions for prisoners.
In the UK, the National Offender Management Service uses polygraph testing for high-risk offenders like convicted sex offenders. These individuals are tested every 3-6 months, with results considered alongside other evidence. Although a failed test does not automatically revoke parole, it may influence decisions regarding their release. Convicted individuals also retain the right to appeal such decisions.
The UK government has proposed expanding this system to include offenders convicted of domestic abuse, adding polygraph testing as a condition of their licence after release.
In the US, polygraph tests play a larger role in parole decisions, particularly for sex offenders. Failure to pass a test can sometimes result in extended prison sentences.
Elsewhere, polygraph tests are also used as investigative tools by law enforcement. In some countries, police use them to eliminate suspects, obtain confessions, or generate new leads. While this approach is not currently practiced in the UK, some experts, like Don Grubin, Emeritus Professor of Forensic Psychiatry at Newcastle University, have advocated for its adoption.
“There is a real reluctance to use [polygraph testing] in investigations for reasons that I think are irrational,” Professor Grubin told The Independent in 2015. “If it is used as part of a thought-through strategy, it helps you eliminate suspects and gain numerous other leads.”
Conclusion
Lie Detectors UK highly recommends Regan Peggs Solicitors as a forward-thinking law firm leading the way in their industry. Whether you’re curious about the legal use of polygraph tests or exploring their broader applications, understanding their strengths and limitations is essential for navigating today’s legal landscape.