To tell you the truth, I was a doubter - but my lie caught me out... We put a Herts police polygraph test under the spotlight, and it comes up trumps

Tell the truth: Taylor Geall is wired up for the test

Tell the truth: Taylor Geall is wired up for the test - Credit: Archant

Fight, flight or freeze – that’s how the experts talk about the body’s response to stress.

The Hollywood view of lie detectors - Robert de Niro and Ben Stiiller In Meet The Parents

The Hollywood view of lie detectors - Robert de Niro and Ben Stiiller In Meet The Parents - Credit: Archant

And even if you’re strapped in a machine which is monitoring your reactions and neither of those three options is a practical response, the way they make your body change reveals a lot about you.

Polygraph examiner Tim Benson sets the scene: “If you’re walking down an alleyway late at night and you hear a bang somewhere in the distance, even momentarily, your body is going to be experiencing some level of stress.

“When something like that happens, changes are taking place in your body that you can’t control – heart rate, sweat rate, these happen automatically.

“When you tell a lie, your body responds in a similar way.”

Tim is one of two polygraph examiners now working with the police in Herts, which is one of only two forces in the UK which make use of polygraph machines, more famililiarly known as lie detectors.

The force has carried nearly 120 tests since they were introduced in the summer.

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The results can’t be used as evidence in court, but they can help officers come to a decision about whether they can trust in someone’s promises about their future behaviour.

That means convicted sex offenders, as well as those accused of downloading indecent images of children, can be asked if they are prepared to take the test.

The aim is to minimise risk. Those applying to be removed from the sex offenders register, for example, will be asked to take a polygraph test as part of that procedure.

Tim says: “We don’t force them but a lot of people say yes, which is good for us because it helps us build trust.”

If somebody refuses to take a test, it is not held against them, although Tim says: “We would be concerned if they said no – we’d be curious as to why that was.”

The tone of the examinations, Tim tells me, is informal. He says: “We spend a lot of time explaining to people how it works and some of the science behind it.

“A lot of people turn up and say: ‘This is like being on Jeremy Kyle’.

“Or people say they’re going to beat it – normally by the end of it they’re not very sceptical.”

Sceptical? That’s part of my stock in trade.

When Tim told me that whenever I lied, there would be telltale responses on the screen, I saw it as a challenge.

I was cued up for what’s known as the ‘acquaintance test’.

Tim asked me to think of a number between three and eight and write it in the middle of a piece of paper.

Starting at the top of the page, Tim then wrote three, four, five, and under my six, the numbers seven and eight to that the numbers featured in a vertical line.

Tim then told me to answer truthfully, and asked whether I had written the number three, four, five and so on.

He explained: “That’s what we’re going to do on the test, except on the test I want you to say no to every question, including number six.

“When we get to number six, you’re going to lie to me. You’re going to say ‘no’ to every single question.”

Then we set about plugging me in to the lie detector.

Two of my fingers were strapped up in metal plates to measure my ‘galvanic skin response’ – that’s how much I perspired to you and me.

Another device measured my heart rate and I had two ‘pneumographs’ wrapped around me, one on my chest (for my breathing), one on my stomach – for the gastric fibs, I presumed.

I also had a blood-pressure monitor on one arm and I sat on a pad which measured my movement.

Tim switched on the machine and began asking questions.

“Regarding the number that you wrote,” he said. “Did you write the number three?”

“No,” I replied. This is going to be a cinch, I thought.

“Did you write number four?”

“No,” I said, feeling the lie approaching.

“Did you write the number five?”

“No.” I could feel my pulse rise under the weight of the impending lie.

“Did you write the number six?”

“No,” I said and heard the blood pulse in my ears. I felt the blood-pressure monitor tighten, too.

Tim asked about seven and eight, but it was too late. I’d given the game away. I’d blown it.

The graph showed a steady incline of my heart rate and a spike in my galvanic skin response as Tim asked about six, showing beyond doubt where I had lied.

My scepticism dissolved. If my body had such a response to an inconsequential lie, then how must those people who have a lot riding on the strength of their answers react?

Polygraphs are likely to be rolled out to more forces around the country and Tim, who had three months of training in order to use it, says he has no doubts about the method’s accuracy and has every confidence that it is helping officers make the right calls.

Maybe that Jeremy Kyle chap has been on to something all along.