The criminal justice system of England and Wales increasingly deploys the polygraph to extract information from released offenders. Although there is little judicial authority regarding the admissibility of polygraph evidence, we should not misinterpret silence as legal uncertainty. The paper will, first, show that the central claim for the understanding of the polygraph—i.e. the presupposition that the polygraph indicates deception—is inextricably linked to an obsolete paradigm in psychology (Introspection). Secondly, I will turn to first principles in the law of evidence, especially the general ban on opinion evidence and the requirement for scientific validity. The requirement that expert evidence has a sufficiently reliable scientific basis explains why polygraph evidence cannot be adduced at the criminal process. Thirdly, I will draw attention to the use of polygraph tests in the context of probation, pursuant to the Offender Management Act 2007. With the use of the polygraph, the criminal justice system does not only infringe the released offender’s human rights, but also fails to protect the public. The combination of inadmissibility of the polygraph in the criminal process and its use from probation services creates thus a major contradiction which is detrimental to the integrity of the legal order.