The justice secretary has defended a proposal to give terrorists lie detector tests to prove they have reformed and are not planning to carry out another attack.

Plans to introduce “polygraph testing” were announced by the government as part of a wave of measures being described as a “major overhaul” in the way terrorists are punished and monitored, including tougher sentences to see them locked up for longer.

It is understood there are hopes terrorists who are going to be out on licence could be made to take the test in a similar way to which sex offenders are sometimes questioned to check their behaviour.

Robert Buckland said the tests could be an effective risk assessment tool, despite having accuracy rates as low as 60%. 

“Lie detectors have already been introduced in assessing the risk posed to the public by sex offenders, they came in about seven years ago,” he told BBC Breakfast.

“They’re not part of the criminal investigation or evidence one might hear in court. It’s all about the authorities assessing the risk posed to the public by offenders.

“This is not a new concept. I think it is a sensible measure in order to help maximise the understanding of the risks that some of these prisoners pose to society.”

Pressed on the accuracy of the tests, he told Sky News: “I’m not pretending on their own, polygraphs, lie detectors, are the be-all-and-end-all, which is why what we are also doing is doubling the number of specialised counter-terrorism probation officers… improving training, getting more psychologists in there, specialist imams as well will be working with these people.”

“We get a lot of people who are superficially very compliant with the regime and sometimes the assessment of risk is a really difficult thing to do.”

“You can get people who are in effect sleepers for many years and then suddenly back come the hatreds and the prejudices and we see atrocities like the one we did at Fishmongers’ Hall.

However the measure has been dubbed the “Jeremy Kyle” method by some critics. 

More details of The Counter Terrorism (Sentencing and Release) Bill have been released after plans for change were put in place in the wake of the latest London Bridge attack and later announced during the Queen’s Speech.

It is less than two months since convicted terrorist Usman Khan embarked on a killing spree armed with two knives and wearing a fake suicide vest after attending a prisoner rehabilitation programme near London Bridge.

Describing the move as a “major shift” in the UK’s approach to the sentencing and management of terrorist offenders, the announcement from the Home Office and the Ministry of Justice (MoJ) also promised to force dangerous terrorists who receive extended determinate sentences to serve the whole time behind bars.

Other measures include doubling the number of counter terrorism probation officers, scrapping early release from jail for those classed as dangerous and ensuring those convicted of terrorism offences spend a minimum of 14 years in jail.

Plans have also been made to give an immediate £500,000 cash injection for support for victims of terrorism. 

Terrorists deemed not to be a risk would have to serve two-thirds of their sentence before the Parole Board could consider them for release.

Jonathan Hall QC, the independent reviewer of terrorism legislation, will also review the way in which agencies like the police, probation and security services investigate and monitor terrorists – known as Multi Agency Public Protection Arrangements (Mappa).

Home Secretary Priti Patel said: “The senseless terror attack at Fishmongers’ Hall in November confronted us with some hard truths about how we deal with terrorist offenders, which is why we immediately announced a review into sentencing and licence conditions, to do whatever is necessary to stop these sickening attacks from taking place.

“Today we are delivering on those promises.”

Plans for the Bill were first mooted shortly after the November attack, which claimed the lives of Saskia Jones and Jack Merritt.

At the time Merritt’s father Dave hit out at Boris Johnson, accusing him of seeing an opportunity to score political points during the general election in the aftermath of the tragedy.

Khan, a 28-year-old British national from Staffordshire, had been released from prison on licence in December 2018, halfway through a 16-year prison sentence after he was convicted of terror offences in February 2012.

He was part of an al Qaida-inspired terror group, linked to radical preacher Anjem Choudary, that plotted to bomb the London Stock Exchange and build a terrorist training camp on land in Pakistan-controlled Kashmir owned by his family.

Staffordshire Police is being investigated by the Independent Office for Police Conduct for its role in managing Khan.

In the year to the end of September, there were 44 convictions for terrorism offences, with 17 offenders being sent to jail for between four and 10 years, the Government said.

Five were jailed for 10 years or more and one was handed a life sentence.

Around 245 convicted terrorists were freed from jail between 2012 and 2019.

Shadow home secretary Diane Abbott said the announcement of a security overhaul was “an admission of failure” by the government.

“Major terrorist outrages have occurred all too frequently, including attacks by perpetrators who were known to the security services,” she said.

Liberal Democrat home affairs spokeswoman Christine Jardine said judges already had the power to lock up terrorists for life while polygraphs were “not accurate or reliable enough” for such critical decisions.

“We will continue to oppose authoritarian laws that do little to make us safer, but a lot to undermine essential British freedoms,” she said.