Why was the London Bridge terrorist released from prison?

Was Usman Khan still serving a prison sentence at the time of the London Bridge attack? What had he done?

Khan was convicted in 2012 in a complex court case involving three connected al-Qaida inspired groups. He was one of three men from Stoke-on-Trent who were convicted of planning to set up a terrorist camp in Pakistan, and had planned to travel there to carry out attacks in Kashmir.

Khan, 28, was released from prison on licence last year. At the time of the attack he wearing an electronic tag, managed by the probation service and subject to low-level monitoring.

What sentence did he originally receive?

Khan was originally sentenced in February 2012. Like the other Stoke plotters, he pleaded guilty. The trial judge, Mr Justice Wilkie, weighed up whether to give Khan a fixed, determinate sentence, which under the prevailing rules would have meant he was eligible for release halfway during his prison term, or an indeterminate imprisonment for public protection (IPP) sentence, which would have meant his release would be subject to a parole board review.

He concluded that Khan and two others posed a sufficiently long-term risk to the public to hand down an indeterminate sentence. “In my judgment,” Wilkie concluded, Khan and the other two Stoke plotters were “more serious jihadis than the others. They were working to a long-term agenda”.

What happened when the case went to the court of appeal?

Khan and the other Stoke plotters successively appealed against their indeterminate sentences in a case that concluded in March 2013.

The court of appeal, chaired by Lord Justice Leveson, concluded that there was no suggestion that Khan or the other two “would be in a position to activate, operate or participate” any terror training facility in Pakistan, and formed the view that in any event, their terror plans were largely related to overseas.

The court decided to impose fixed sentences instead. In Khan’s case this new sentence was a fixed term of 16 years, extended by a further five on licence. That meant he would automatically be allowed out after eight years, without the involvement of the parole board.

Why were such dangerous prisoners let out without parole board oversight?

The type of prison term Khan ultimately received was an extended sentence for public protection (EPP). These were introduced in April 2005, by Labour, in the Criminal Justice Act 2003, alongside the IPP sentences.

Initially, both required that a parole board assessment be made before a prisoner could be released. But the prison population soared, partly because parole boards were not impressed by rehabilitation efforts in jail.

Related: Usman Khan profile: terrorist who wanted to bomb London Stock Exchange

Labour changed the law in 2008 to ease the pressure and for extended sentences only the requirement for parole board oversight was removed. Prisoners like Khan – who were not subject to any other conditions – became automatically eligible for release halfway through their jail terms.

The rules for terrorism sentencing were changed by the Conservatives in 2015 as Islamic State became more active. All terrorism offenders sentenced since then have to apply for parole.

So is Boris Johnson right to blame Labour?

No. It is true that Labour’s law change of 2008 created the type of extended sentence that allowed Khan to be released automatically. But Labour had also created a viable alternative, in the indeterminate IPP sentence, which required parole board oversight.

The Conservatives election manifesto says: “We will introduce tougher sentencing for the worst offenders and end automatic halfway release from prison for serious crimes”, but it has nothing specific on terror offences. Johnson’s post-attack proposal that terrorists should spend at least 14 years in prison is entirely new.

Is anybody to blame?

It is easy to talk about blame with the benefit of hindsight but difficult to apportion it in reality. Labour had given the judges at the time a choice: an indeterminate sentence requiring parole board oversight or a determinate sentence, which did not.

Mr Justice Wilkie chose the first, and the court of appeal overturned his decision and chose the latter. Recent law changes by the Conservatives have only reduced the discretion available to judges in terror cases.