A former reviewer of terrorism has said government plans to extend prison sentences for terror offenders is "certainly going to be challenged."
Lord Carlile, ex-independent reviewer of terror legislation, has raised concerns about new legislation, which will review whether the current maximum sentences for terrorist offences is sufficient.
He said the plans "may be in breach of the law."
The new rules would apply to prisoners who have already been sentenced and would ensure that extremists are closely monitored on release.
His comments come after Streatham attacker, Sudesh Amman, stabbed two people 10 days after he was released halfway through a prison sentence.
On Monday, Justice Secretary Robert Buckland said emergency legislation is needed to make sure terrorists are not released automatically from prison half way through their sentence.
Mr Buckland said offenders will not be considered for release until they have served two-thirds of their sentence and no terrorists will be released before the end of their full custodial term unless the Parole Board agrees.
The Parole Board would be “strengthened” to deal more effectively with the risks that terrorists pose and steps would be taken to introduce the plans “as soon as possible”, he said.
"I think it may have gone too far," Lord Carlile told BBC2’s Newsnight.
"The decision to lengthen the sentences of people who have already been sentenced, and therefore expected to be serving half the sentence the judge imposed upon them, may be in breach of the law.
"It is certainly going to be challenged."
Meanwhile ITV's This Morning presenter Holly Willoughby asked Home Secretary Priti Patel, "how safe are we?" following the recent terror attack.
Ms Patel said: "We are safe."
Discussing the recent terrorist attacks in Streatham and London Bridge, Ms Patel said: "Those two individuals did not go up in front of anybody… they did not go through a parole board process.
"They were not assessed, they were not checked over essentially.
"They were not assessed on their conduct in prison and if they were suitable to be released.
"My own view, and the Prime Minister agrees as well, we cannot keep having terrorist offenders… we’ve got to stop that, we’ve got to stop them from having early release and this automatic release where they’re not checked and they’re not sitting in front of a parole board."
Amman, who attacked two people on a busy London street, was released from prison despite reportedly telling a fellow inmate that he wanted to murder an MP.
He was shot dead by police around a minute after launching an attack on two bystanders in Streatham High Road, south London, on Sunday. A third person was injured by flying glass during the gunfire.
A man in his 40s is in a serious, but stable condition, a woman in her 50s has been discharged from hospital and a second women, in her 20s, who suffered minor injuries has also left hospital.
Police said he began stabbing the victims about 60 seconds after entering a shop, where he stole a knife and removed the packaging as he ran from a staff member.
The 20-year-old, who was jailed for possessing and distributing terrorist documents in December 2018, was freed from prison less than a fortnight ago and had been staying at a bail hostel in nearby Leigham Court Road.
A former prisoner who spent time with Amman in Belmarsh high-security prison told The Times: “The guy was definitely insane and he never hid his intentions, so it’s crazy how he even got out of jail.”
The man said Amman wanted to copy the murder of MP Jo Cox and told him “the only way to get these filthy kafirs (non-believers) out of Syria is to take out MPs like that white guy did with the lady in 2016,” The Times reported.
The former inmate told the newspaper that Amman “wanted to do something real, something organised like the (IRA) used to do”.
IS supporter Amman, who at the time of his sentencing was 18 and living in Harrow, smirked as he was jailed for three years and four months at the Old Bailey in December 2018.
The Metropolitan Police said he was released from prison on January 23 2020.
Scotland Yard said armed officers were following Amman on foot as part of a “proactive counter-terrorism surveillance operation” when the incident took place.
Jack Merritt and Saskia Jones were killed by a convicted terrorist who was released early from prison.
Usman Khan went on a killing spree on November 29 during a prisoner rehabilitation programme.
Khan, armed with two knives and wearing a fake suicide vest, killed the University of Cambridge graduates in the attack.
He was convicted of planning to bomb the London Stock Exchange in February 2012, but released from prison on licence in December 2018, halfway through his 16-year prison sentence.