The Government has recently announced plans for mandatory lie detector (polygraph) testing for convicted sex offenders to be rolled out across England and Wales following a successful pilot scheme.  It is proposed that those eligible for release on licence would have to undergo a test in addition to the conditions already required.

The two year pilot test was carried out in the Midlands between 2009 and 2011 and involved over 300 convicted sex offenders.  It found that when lie detectors were used offenders were much more likely to make admissions to probation staff.  Offenders themselves also reported that the lie detectors assisted them in managing their own behaviour.

Ministers are now considering how compulsory polygraph tests could be rolled out to provide probation officers with more information to manage the most serious sex offenders. The proposals could result in some offenders being recalled to prison should the test results and other information indicate that they have broken their conditions or present a risk to public safety.

Whilst some may welcome these proposals, they also raise significant concerns. Although polygraph evidence can be admitted in court by agreement and at the trial judge’s discretion in a number of American states, and is frequently used by US law enforcement agencies in forming decisions about whether to pursue an investigation, its purported reliability has been the subject of much debate and scientific challenge. Tests measure blood pressure, heart rate, breathing and levels of perspiration of the subject and it is for the administrator to then assess whether the individual is telling the truth. A number of concerns have been raised about their misinterpretation or misuse by both the administrators and the subjects leading to fears of unreliability, and critics claim that the tests have no scientific validity.

It is not currently an admissible form of expert evidence in any part of the UK criminal justice system because it is not considered sufficiently reliable.

There is a fundamental unfairness at the heart of these proposals. Whereas polygraph evidence is considered too unsafe for use in criminal proceedings, its use is now to be allowed in tests, failure of which may lead to longer periods in custody.

It is surely wrong to allow a form of assessment that is the subject of such criticism and argument to have any place in the management of prisoners, and there is a danger that once polygraphs are used in one form of decision making this will open the door for their use in other circumstances.

If the government is serious about these proposals then it should put more resource into assessing the reliability of the polygraph test as a measure of truthfulness.