LONDON — The British government said on Tuesday that it would toughen terrorism sentences and end early release for serious offenders, following through on promises made by Prime Minister Boris Johnson in November after a convicted terrorist who had been automatically released carried out an attack that killed two people near London Bridge.
The attacker, Usman Khan, 28, who was released in December 2018 after serving eight years of a 16-year sentence for his involvement in a bomb plot, began a knife attack while attending an event on prison rehabilitation at Fishmongers’ Hall, a central London conference venue. Wearing a fake explosive vest, he fled over the nearby bridge, and he was shot and killed by the police shortly afterward.
The attack, during the final weeks of a British general election campaign, set off a heated debate over jail sentences for convicted terrorists and their overall reintegration into society.
Under the new legislation, which could be introduced in Parliament this spring, terrorism offenders would serve a minimum of 14 years in prison. The number of probation officers specializing in counterterrorism would be doubled, and the counterterrorist police would receive a 10 percent funding increase, the British Home Office, the government department responsible for policing and national security, said in a statement.
“The senseless terror attack at Fishmongers’ Hall in November confronted us with some hard truths about how we deal with terrorist offenders,” Home Secretary Priti Patel said.
Justice Secretary Robert Buckland said that law enforcement officers could also use lie detectors on terrorism offenders in order to better assess possible threats. The reliability of polygraph testing is often disputed, but Britain already uses it with some sexual offenders — though the use that can be made of the results is limited and they are not admissible in British courts.
“We get a lot of people who are superficially very compliant with the regime,” Mr. Buckland told the British broadcaster Sky News, referring to terrorist offenders in prison. “You can get people who are in fact ‘sleepers’ for many years and then suddenly back come the hatreds and the prejudices.”
While in jail, Mr. Khan had assured officials in letters that he wanted to follow a deradicalization program and that he no longer embraced radical views. He had been given an indeterminate sentence in 2012 for his involvement in a terrorist cell that planned to bomb the London Stock Exchange, which was later replaced by a 16-year fixed-term sentence.
Referring to Mr. Khan and two other defendants in the same case, a judge said in 2012 that “these offenders would remain, even after a lengthy term of imprisonment, of such a significant risk that the public could not be adequately protected by their being managed on license in the community.”
David Videcette, a former antiterrorism detective, said on Tuesday that some of the proposed changes were incremental, such as the use of lie detector tests, while others, like more funding for counterterrorism police, seemed more urgent.
He said the domestic terrorism landscape had changed, with fewer “large scale attacks, and more lower-tech ones.”
“The individuals involved in them are much harder to catch because they don’t always interact with wider networks,” Mr. Videcette added. “So it’s more labor intensive to monitor them and potentially catch them.”
Several European countries have been grappling in recent years with their response to the threat posed by radicalized individuals who may carry small-scale attacks on their own, or regroup with larger cells. They have warned that zero-risk situations do not exist, while trying to reassure a wary public with additional funding and tougher security measures whose impact often takes years to assess.
In France, officials have reinforced intelligence resources in prison to monitor soon-to-be-released inmates, as a majority of its 500 terrorist convicts and more than 1,200 inmates suspected of radicalization are scheduled to leave prison within the next few years.
After the November attack in London, politicians on both ends of the spectrum accused their opponents of having slashed resources dedicated to the monitoring of convicted terrorists.
It was also seen as an echo of a terrorist attack near London Bridge in 2017 that left eight people dead, also during the closing stages of an election campaign. The political response to that attack included a focus on cuts to police numbers under Mr. Johnson’s predecessors, David Cameron and Theresa May — cuts that Mr. Johnson began his own campaign by promising to reverse.
“I have long argued that it is a mistake to allow serious and violent criminals to come out of prison early,” Mr. Johnson said in November, as he announced that the security services would review the parole conditions of 74 people who had been convicted of terrorism and released early. Mr. Johnson was later accused of exploiting the attack for political gain, including by the father of one of the victims.
David Merritt, the father of Jack Merritt, a rehabilitation worker who was killed by Mr. Khan, said that his son would have been furious at Mr. Johnson’s response to the attack.
“He would be seething at his death, and his life, being used to perpetuate an agenda of hate that he gave his everything fighting against,” Mr. Merritt wrote of his son in The Guardian.
On Tuesday, Mr. Merritt called the potential use of lie detectors on convicted terrorists “a cynical, headline-grabbing gimmick to distract our attention.”