Use of polygraph tests during the pre-charge investigation stage

Written 3rd April 2024 by Nicola Bruce

We have experienced a number of clients being asked to participate in a polygraph test, which is raising concern that the police appear to be increasing the use of polygraph tests at the investigation stage.

If you find yourself being asked to take part in a polygraph test, this article explains why the police are using them.

What is a polygraph test?  

A polygraph test is what has been referred to as a ‘lie detector test.’ It works by measuring the physiological changes in the body when the individual is asked certain questions. It measures breathing, heart rate and blood pressure. Sweat and changes in the individual’s normal rates can indicate (or suggest) if an individual is attempting to deceive. 

Are polygraphs used in England and Wales?  

Yes, they are. A polygraph examination will be offered to certain individuals, subject to a police investigation where there is a suspicion of a sexual offence involving children, but this is on a voluntary basis. You do not have to take part in a test.

The polygraph is only mandatory for certain individuals who have been convicted of sex offences, domestic abuse, or terrorism as part of their parole condition.  

What is the history of polygraph examinations in England & Wales?  

Polygraph examinations were piloted in England and Wales in 2007 and, in 2008, a 3-year study commenced with the Probation Service evaluating the mandatory use of polygraph on high-risk sex offenders [section 28 of the Offender Management Act 2008]. Following what was deemed to be a successful pilot, in 2014 legislation made it mandatory for high-risk sex offenders on parole to undergo mandatory testing as part of their conditional release.  

The use of polygraph expanded further following the Domestic Violence Bill, which targets individuals deemed to be high risk of causing harm in a domestic setting [Domestic Abuse Act 2021] and, the Counter Terrorism Bill, which enables mandatory testing for certain individuals who have committed a terrorist related offence [Counter-Terrorism & Sentencing Act 2021]. 

According to the Home Office Impact Assessment on the Criminal Justice Bill [Prisons and Offender Management Equalities Statement] ‘published in November 2023, to date more than 7,000 polygraph tests have been carried out on people convicted of sexual offences and, since the Counter-Terrorism & Sentencing Act 2021, 97 polygraph examinations have been completed with 42 individuals convicted of terrorist-related offences.  

Could you be asked to take part in a polygraph assessment? 

We have broken down the scenarios where a polygraph may be requested into two categories:  

Individuals subject to a criminal investigation [e.g not charged or convicted of an offence] 

Unlike the USA, polygraph questioning cannot be used as ‘evidence’ against an individual to prove guilt at trial as it would amount to inadmissible evidence. Despite this, there appears to be an increase in the use of polygraph examinations at the police investigation stage for individuals arrested on suspicion of sexual offences relating to children. 

There is no framework to prevent police officers from using or attempting to use the polygraph as part of the investigation process. This means that there is nothing to stop the police from asking an individual to take part.  However, taking part in a polygraph examination is not mandatory. It is a voluntary process and will normally be offered at the investigation stage, soon after the police interview. This means an individual has a choice and can either agree or refuse to take part in the polygraph. 

Whilst the polygraph report does not amount to ‘evidence’ that would form part of the prosecution case, it will be shared with the Crown Prosecution Service as ‘sensitive unused material’ as part of the disclosure requirements [Criminal Procedure and Investigations Act 1996]. 

If a polygraph does not amount to evidence, why do the police use it during the investigation stage?

The police will use the polygraph to assess the likelihood that the suspect would re-offend if released on police bail. The results therefore could impact whether a suspect can return to the family home or have contact with his/her children and, ultimately, whether or not the police seek to withhold bail if they deem there to be a high risk of further offending. Also, the police have indicated that they use the polygraph to help prioritise lines of inquiry, for example by establishing the device(s) likely to contain evidence (to save time in digital forensic examinations).  

An online article published by the BBC in January 2023 ‘North Yorkshire Police use lie detector tests for sex offenders’ reported that lie detector tests were being used by North Yorkshire Police to investigate sex offenders and referenced comments made by Detective Superintendent Whorriskey that the polygraph was being used quite significantly where offenders were using communication devices further communication with children and police are able to use the polygraph information to help them prioritise the offender’s devices for examination within the digital forensic unit.  

At the investigation stage, it is essential that legal advice is obtained as to whether taking part in a polygraph examination and whether doing so would benefit your case.   

Convicted individuals  

The Probation Service use polygraph examination to manage people convicted of sex offences, domestic abuse (where there is deemed to be a high risk of serious harm and thirdly, those who have committed ‘relevant’ counter-terrorism related offences and who fulfil certain other statutory and policy criteria will be subject to mandatory polygraph assessments.  

The Police Crime Sentencing and Courts Act 2022 filled certain gaps in the regime in relation to updated sex offences, service offenders, and offenders serving sentences imposed outside England and Wales.  

Could a person be recalled to prison for failing the polygraph examination?  

No, people on supervision cannot be recalled to custody if they fail a polygraph test.

But they could be recalled if one of the following scenarios is identified: 

  • Making disclosures during the test that amounts to a breach of other licence conditions or that their level of risk has risen whereby they can no longer be managed by the Probation Service safely in the community.   
  • If an individual attempts to trick the polygraph test or refuses to take part in it, then the individual could be recalled to custody.  

Failing a test could also result in more frequent testing taking place; a formal warning could be given, or additional conditions added to the licence.  

Can polygraph evidence for convicted individuals be used in court?  

No. Information from a polygraph test cannot be used in criminal courts as evidence against the released individual, but it could be used in civil courts at the judge’s discretion.  

Who carries out a polygraph test?

Only trained professionals will carry out a polygraph test. As part of a parole condition, the polygraph test will be carried out by experienced qualified Probation Officers who have been trained as accredited examiners to the standards set by the American Polygraph Association (APA) and who are also experienced in managing high-risk individuals.

Police officers with relevant training will carry out the test at the investigation stage.  

Due to the increased use of the polygraph, the College of Policing in 2022, made recommendations that it took on the role of Polygraph Schooling and developed a set of standards for polygraph practitioners including training and accreditation. This appears to

be due to the expansion of police use of polygraph and the lack of requirements and standards for police use and practice. Whilst the police taking control of polygraph assessments would ensure set standards and requirements are met which would help to ensure compliance, assurance, and uniformity across police forces, it could also encourage further expansion of its use. 

How accurate are polygraph examinations?  

According to the government public publication on polygraph testing in 2022, polygraph testing is 80-90% accurate.  

The use of polygraph still attracts much criticism. The use of polygraph remains a contentious debate.

Dr. Kyriakos N Kotsoglou from Northumbria University described the use of polygraphs as “Zombie forensics” and referred to the test’s lack of consistency, stating that they were used deception and psychological manipulation to convince the subject that the polygraph works.  Dr Kotsoglou added

“Its purpose and sole potential are not to detect truth, but to enable interviews to extract confession statements at the price of rationality and legitimacy” [ 27/01/2023].  

Despite criticism, it appears that plans to extend the use of polygraph continues.

How can Olliers help you?

Olliers team of specialist lawyers has extensive experience in representing individuals at the police station and throughout the police investigation stage through pre-charge engagement. Our lawyers will represent you during the interview and throughout the investigation and provide you with expert legal advice regarding whether you should agree to take part in a polygraph examination and liaise with the police on your behalf. 

We understand that being subject to a criminal investigation is a stressful and anxious time. Our lawyers will ensure that you have a clear understanding of your rights, what is in your best interests, and the consequences and benefits of options. Olliers team are specialists in this area and will ensure that your best interests are put first.

Nicola Bruce

Nicola Bruce

Senior Associate


Head Office


Satellite Office

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