True or False: Do lie detector tests work and are they be able to prevent terrorist attacks?

Plans have been announced to introduce lie detector tests - known as polygraph tests - to assess if terrorists have reformed and no longer pose a risk.

But many disagree the style of testing, first seen in 1921, is accurate enough to determine if a subject is lying.

Director of UCL Institute of Cognitive Neuroscience Professor Sophie Scott told ITV News: "You can't use a polygraph to work out if somebody is lying or not.

"Because actually there's no one thing that people, their bodies or their brains do when they're lying that we can scientifically identify and say 'right then, there, a lie happened'."

Lie detectors measure changes in things such as heart rate, breathing and even sweat on the skin. Credit: ITV News

Polygraph, which translates to 'many measures', can note changes in a person's heart rate, their breathing and even how sweaty their skin is - something the Ministry of Justice has used to check the behaviour of sex offenders since 2014.

But scientists have never been able to say for sure if this data proves a person is telling a lie.

According to Prof Scott, who has worked in the area for over 30 years: "I think the bigger problem is that while it may tell you that somebody is in an emotional state, what it does not tell you is why they are in that emotional state.

"There is often the idea that you could game this - you might hold your breath or try and increase your heart rate some other way and I mean you could never rule out the possibility that somebody could do this."

Home Secretary Priti Patel and Prime Minister Boris Johnson visited the scene of the London Bridge terror attack in November. Credit: PA

Currently, the test cannot be used in UK courts because of uncertainty around how accurate the results are.

But Home Secretary Priti Patel plans to roll the technique alongside increasing the number of counter terrorism probation officers, providing specialist psychologists and training front-line prison and probation staff to identify those behind bars and on licence.

The Counter Terrorism (Sentencing and Release) Bill is in response to the recent London Bridge attack committed by convicted terrorist Usman Khan, who was out on licence from prison when he killed Jack Merritt and Saskia Jones.

However, former Head Head of the National Counter Terrorism Security Office Chris Phillips thinks that these measures don't go far enough.

Mr Phillips said: "I don’t think lie detectors on their own will ever be good, we know they can be defeated, everyone knows they can be defeated.

"Lie detectors are one tool in a big tool kit, those other tool kits could be geo-location devices and of course you can tag telephones to see who they’re talking to and what they’re saying, so these are all just parts of a tool kit.

"But of course, all these things are only useful if you’ve actually got the officers, the people to do it and that’s not always the case."