UK police forces rapidly expanding use of controversial lie detector tests
Police forces in Britain have rapidly expanded the use of controversial “lie detector” tests and may be exceeding their powers by using the technology to interview and gather evidence against unconvicted suspects, it can be revealed.
The number of polygraph tests carried out by police in England and Wales last year rose by more than half compared to 2018, with at least 14 forces acknowledging they now use the interrogation technique. Between them the forces carried out more than 700 tests in 2022 – a five-year high, according to data obtained by i and Liberty Investigates.
Despite the accuracy of polygraphs remaining highly contested in scientific circles, information released separately to academic researchers suggests police are also deploying them for uses including helping to decide whether prisoners such as sex offenders or domestic abusers should be returned to prison and assessing the risk posed to children by arrested suspects.
The rapid growth in the use of polygraphs by police comes as the Government is accelerating a broader roll-out of contentious technology to fight crime, including the use of powerful facial recognition software with the potential to check and identify members of the public by cross-referring with passport and driving licence databases.
In the King’s Speech laying out its legislative programme last month, the Government unveiled plans to expand polygraph use and increase existing powers available to probation officers to monitor convicted sex offenders and terrorists.
But the extent of parallel use of the technology by UK police, whose umbrella training body is also setting up Britain’s first “National Polygraph School”, has until now been unclear.
Data obtained by i and Liberty Investigates revealing the rapid increase in police use of “lie detector” machines is accompanied by separate research by experts at Northumbria University showing the tests are being used on individuals who have not yet been convicted of an offence, which may be unlawful and could be subject to legal challenge.
The Northumbria researchers, who found the technique is being used for interviews to help establish whether suspects should be allowed contact with children, expressed concern at the adequacy of safeguards and controls over how police use polygraphs.
The figures disclosed to i and Liberty Investigates under Freedom of Information (FOI) rules show that at least a third of the 43 forces in England and Wales conducted “lie detector” tests, carrying out 710 procedures in 2022 – and likely dozens more, as one force could only provide figures by financial year. This was a rise of at least 55 per cent compared to 2018. Among the forces for which data has been obtained, Essex Police carried out the highest number of tests (99), followed by Suffolk (93 for the financial year 2022-23) and South Yorkshire (87).
A number of forces, including Essex Police and South Yorkshire Police, underlined that their use of polygraphs was restricted to the monitoring of convicted offenders, in particular those subject to tests as a result of sex offences.
However, one unnamed force acknowledged it carries out polygraph testing on “pre-conviction” sex offenders while another said it had considered doing so in the future.
Polygraphs, which are often described as “lie detectors”, have long been used in countries such as the United States and Japan as interrogation tools by measuring certain physiological responses claimed to be associated with the telling of untruths, such as increased sweating or breathing rate changes. Individuals are asked a series of questions and the responses are examined by trained officers for alleged signs of evasion and untruths, as well as new information given up by offenders who might fear failing a test.
But the science behind the machines remains highly contested and evidence obtained from polygraph tests is inadmissible in UK criminal courts. Instead, the tests have been deployed in England and Wales to allow the monitoring of sex offenders by probation teams, and more recently as a condition of release in some terrorism and domestic abuse cases.
It emerged in October that four convicted terrorists have been returned to prison as a result of information given during polygraph tests or failing to comply with an order to undergo an examination. The use of “lie detectors” was introduced for terrorism offences in 2021 after the London Bridge attack two years earlier when Islamist extremist Usman Khan duped probation staff into believing he had reformed and went on to murder two Cambridge graduates during a rehabilitation conference.
Concerns over potential unlawful use of ‘lie detectors’
Experts have expressed concern over the legal basis being used by police to conduct polygraph tests.
How is the technology used by the UK’s probation service?
Probation teams in England and Wales have been using the interrogation technique under national rules set out in 2014 to monitor sex, domestic abuse and terrorism offenders.
A significant proportion of the most serious offenders in these categories can have a requirement to undergo regular polygraph testing imposed as a condition of release from prison under licence. Under the new Criminal Justice Bill, polygraph testing is set to be extended to murderers judged to pose a risk of committing a sexual offence on release.
If an offender is judged to have “failed” a test, or provides new information of concern, this can trigger further investigations potentially resulting in a recall to prison.
What is an example of how the Government says polygraph testing is used and how it can prevent or detect further offences?
J is a 47-year-old man convicted of the sexual abuse of young boys.
He has a licence condition not to have contact with children under the age of 18 years.
J was subject to mandatory polygraph testing as part of his release following a 9 year custodial sentence.
During the polygraph examination he denied any contact with children under the age of 18 years. The test result indicated deception.
The polygraph examiner contacted the probation practitioner who immediately contacted the police. The police were waiting for the offender when he returned to his property and found 3 young boys and another adult in the house.
J was immediately recalled to custody. The police were able to make further investigations.
(Source: gov.uk)
How are polygraphs being used lawfully by police?
Legislation sets out circumstances in which polygraph tests can be used by police, alongside the probation service, to ensure compliance with measures when monitoring convicted terrorists. Lie detector tests can also be set out as requirements for ensuring sex offenders comply with harm prevention orders.
Although no-one can be “forced” to undertake a lie detector test, there are powers within the law which can make regular polygraph monitoring a condition of release from prison for the categories of offenders considered to pose the highest risks of causing harm.
The tests are also used to enforce Terrorism Prevention and Investigation Measures or TPIM notices, which set out restrictions on the behaviour or activity – such as travel, communications or financial transactions – of an individual, either a suspect or a convicted offender, in relation to terrorist offences. Trials are also being conducted on the use of the technology to monitor perpetrators of domestic abuse.
In all cases, police emphasise that the polygraph tests are one of several tools used to assess offenders and new disclosures can serve as the starting point for further investigation by police or the relevant authorities.
How are ‘lie detectors’ being used potentially unlawfully by police forces?
While the use of “lie detectors” by the probation service to monitor convicted criminals is well established in statute, researchers say some police forces appear to be using a less specific, non-statutory parallel testing regime that includes the examination of suspects who have not been convicted.
Dr Kyriakos Kostoglou and Professor Marion Oswald, based at Northumbrian University, pointed to their own FOI findings showing that more than 200 tests have been carried out in the last six years to help decide whether suspects should be allowed contact with children.
Documents disclosed by forces also describe how polygraphs can be used to interview individuals arrested on suspicion of child sex offences such as obtaining indecent images. Under UK legislation, any evidence obtained from a polygraphy test would not be admissible in court.
A briefing paper shared with i and Liberty Investigates by the researchers finds that data and documents released by police forces suggest polygraphs are being used in a “semi-evidential and semi-investigatory way” and as “an interrogation tool”.
Noting a lack of clarity on all the circumstances in which polygraphs are being used, they said that some forces appear to be deploying the technology “beyond published expectations, and in some cases in direct contradiction to published policy”.
When it comes to using polygraph tests for testing individuals who have yet to be convicted of a crime, the researchers added: “There is a high risk that such uses could be subject to challenge as not being in accordance with law… Urgent action should be taken to clarify the legal basis for the many different uses disclosed and those still hidden and redacted… and to ensure appropriate independent scrutiny and oversight.”
Could this type of use be subject to legal challenge?
According to the Northumbria University researchers, the main issue with existing police use of polygraphs is the lack of clarity on the precise circumstances in which they are deployed by forces and the legal structures underpinning or justifying such use.
For example, there are concerns about the suggestion that independent legal representatives are routinely excluded from tests and the extent to which they can be truly described as “voluntary”.
On this basis, there could be grounds for legal challenges to clarify and narrow existing broad powers available to police under common law to use polygraph tests. As the researchers put it: “Our findings raise questions around the lawfulness and procedural fairness of the non-statutory regime [used for some police polygraph tests].”
Cahal Milmo and Mark Wilding
Proponents of “lie detectors” insist the technique has a valid use in law enforcement despite its limitations and often quote a figure that the machines are “80-90 per cent accurate” in picking up the physiological signs of telling an untruth. The American National Academy of Science said studies showed polygraphs were capable of detecting lies at a rate “well above chance, though well below perfection”.
In the UK, police and other law enforcement bodies argue that polygraphs are valuable tools in producing risk assessments about individuals. Rather than being seen as outright evidence of deception, they say “failed” tests should be used only to trigger more intrusive measures such as carrying out a search of an offender’s home or electronic equipment.
Police policy documents acknowledge that the existing legal framework for use of polygraphs is sparse. A paper produced last year for the College of Policing, which sets professional standards for UK forces, noted bluntly: “Currently there are no requirements or standards for police polygraph use.”
When asked about the concerns surrounding the use of “lie detectors”, the Home Office referred enquiries to national policing bodies including the College of Policing.
David Tucker, head of crime at the college, told i and Liberty Investigates that a purpose of its new National Polygraph School is to put in place “standardised learning and development” on the use of the technology.
He said: “Polygraph is not used as evidence in court by police, it is to be used as a tool to assist officers to make judgements about the risk a suspect may pose. Polygraph should also not be used in isolation, but as one of a number of sources of information to assist decision making.”
Dr Kyriakos Kostoglou and Professor Oswald, the experts at Northumbria University, said policing leaders need to seize the opportunity to tackle multiple concerns about existing arrangements, including the fact that legal representatives, who would ordinarily be present at police interviews, are excluded from any polygraph examination.
The researchers said: “The College of Policing’s work provides an ideal opportunity to conduct a full and independent review of all uses of polygraph testing involving police forces. Attention must be paid to scientific validity and to the evidential and procedural safeguards surrounding these uses.”
