Extremists convicted of planning terrorist attacks should be given automatic life sentences, an independent watchdog has said.

Jonathan Hall QC, the independent reviewer of terrorism legislation, was speaking after an inquest jury concluded a litany of failings contributed to the unlawful killings of Jack Merritt, 25, and Saskia Jones, 23, at the hands of convicted terrorist Usman Khan.

The senior lawyer said it was “quite clear” that Khan, who served eight years in jail for plotting to set up a terror training camp in Pakistan, was not safe for release.

He warned that a similar attack by another released terrorist could not be ruled out and called for better sharing of information, including that held by the Security Service, to assess the risks posed by extremists once they are let out of prison.

“I think it’s hard to underestimate how serious Usman Khan’s original offence was.

“He wanted to set up a training camp in Pakistan, to train terrorists to come back and kill people in the UK,” Mr Hall told BBC Radio 4’s PM.

“My own view is that people who are convicted of attack planning should be given automatic life sentences and only released, if at all, when safe.”

Mr Hall added: “I think it’s a shame that the law hasn’t gone in that direction.

“Parliament has just changed the law on terrorism sentencing, but they didn’t include that sort of provision.”

He said the Government was acting to address the management of offenders following a review he carried out last year “and I very much hope that what I found, which was the inability to share information, is going to be deeply remedied”.

Mr Hall said an “agile core group of practitioners” with the “right security clearances” should be involved in managing offenders in the community.

MI5 should be more confident about sharing information of an “official sensitive” nature, below the highest levels of classification, “rather than feeling it’s too secret to share”.

Ms Jones and Mr Merritt were stabbed by Khan at an alumni event put on by Learning Together, a prisoner education programme, on November 29 2019.

Mr Hall warned that a similar attack could not be ruled out.

“Well, it can happen again.

“I mean, reoffending by terrorist offenders is extremely rare but you can’t guarantee that they won’t reoffend,” he said.

“When terrorist offenders are released, they will live amongst us.

“And they will be on licence for many, many years.

“And the authorities will never be able to completely exclude the possibility.”