The home secretary Priti Patel has blamed a previous Labour government for the release of the London Bridge attacker who had been deemed dangerous, as the parties rowed over who was responsible.

Jeremy Corbyn, the Labour leader, said questions need to be urgently answered over the roles of the Parole Board and probation services.

But Ms Patel said the Parole Board had not been involved in the decision to free Usman Khan, who killed two people and wounded others in a knife attack on the bridge on Friday.

Khan was freed from jail on licence last December, having served less than seven years of his sentence.

Ms Patel, who had earlier visited the scene of the attack with the prime minister, posted a link to a news article and tweeted: “The Parole Board could not be involved in this decision, jeremycorbyn.

London Bridge attack: Terror police shoot man after stabbing Show all 29 1 /29 London Bridge attack: Terror police shoot man after stabbing London Bridge attack: Terror police shoot man after stabbing Bystanders and police surrounding a person at the scene of an incident on London Bridge HLOBlog/PA London Bridge attack: Terror police shoot man after stabbing Police and emergency services PA London Bridge attack: Terror police shoot man after stabbing Armed police on London Bridge Twitter London Bridge attack: Terror police shoot man after stabbing A bystander holding a knife after police surrounded a person at the scene HLOBlog/PA London Bridge attack: Terror police shoot man after stabbing People fleeing from Borough Market PA London Bridge attack: Terror police shoot man after stabbing Police during the incident Twitter London Bridge attack: Terror police shoot man after stabbing A white truck across part of London Bridge SophK05/PA London Bridge attack: Terror police shoot man after stabbing A British Transport Police officer runs after reports of an incident Getty London Bridge attack: Terror police shoot man after stabbing Boats from the Metropolitan Police Marine Policing Unit patrol near the scene Getty Images London Bridge attack: Terror police shoot man after stabbing A lorry on the bridge crosses over lanes Luke Poulton via Reuters London Bridge attack: Terror police shoot man after stabbing Members of the police and emergency services arriving at Monument tube station AFP via Getty Images London Bridge attack: Terror police shoot man after stabbing Members of the public held behind a police cordon Getty Images London Bridge attack: Terror police shoot man after stabbing Police at the scene PA London Bridge attack: Terror police shoot man after stabbing Police evacuate people from Borough Market AP London Bridge attack: Terror police shoot man after stabbing Police surrond a part of the bridge Timothy Johnson/Twitter London Bridge attack: Terror police shoot man after stabbing A person is assisted after falling when Police evacuated people from Borough Market AP London Bridge attack: Terror police shoot man after stabbing A Police Officer cordons off London Bridge Station Getty Images London Bridge attack: Terror police shoot man after stabbing Members of staff are ushered into a Fitness First gym Getty Images London Bridge attack: Terror police shoot man after stabbing Handout photo taken with permission from the twitter feed of @ShashD of police at the scene of an incident on London Bridge in central London. PA Photo. Issue date: Friday November 29, 2019. See PA story POLICE LondonBridge. Photo credit should read: Shash/Twitter/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. Shash/Twitter PA London Bridge attack: Terror police shoot man after stabbing People head away from the vicinity of Borough Market PA London Bridge attack: Terror police shoot man after stabbing Office workers look out of a window at a scene EPA London Bridge attack: Terror police shoot man after stabbing Armed police at the scene of an incident on London Bridge in central London. PA Photo. Picture date: Friday November 29, 2019. See PA story POLICE LondonBridge. Photo credit should read: Dominic Lipinski/PA Wire Dominic Lipinski PA London Bridge attack: Terror police shoot man after stabbing Men in forensics suits walk away from the site REUTERS London Bridge attack: Terror police shoot man after stabbing People are evacuated from London Bridge PA London Bridge attack: Terror police shoot man after stabbing ArrowontheHill ArrowontheHill/Twitter London Bridge attack: Terror police shoot man after stabbing Police at the scene of an incident on London Bridge PA London Bridge attack: Terror police shoot man after stabbing Armed police on the scene Alexandra Carr /SWNS.COM London Bridge attack: Terror police shoot man after stabbing Buses on London Bridge during the incident AFP via Getty Images London Bridge attack: Terror police shoot man after stabbing Police on the scene @joebxggs /SWNS.COM

“Your party changed the law in 2008 so that Khan was automatically released irrespective of the danger he posed. Very concerning that you want to be PM but don’t understand this.”

The Parole Board has said it had no involvement in his release and that Khan “appears to have been released automatically on licence” halfway through his sentence.

Khan and two others were originally given indeterminate sentences with a minimum term of eight years behind bars but on appeal the indeterminate sentences were dropped in 2013, making him eligible for release under licence.

Labour’s Yvette Cooper, chair of the home affairs select committee, had tweeted questions about Khan’s release, saying: “Usman Khan was sentenced for serious terror offence in Feb 2012. Thought to be so dangerous by judge he was given IPP sentence to prevent release if still serious threat.

“Instead he was released 6 yrs later without Parole Board assessment. How cd this be allowed to happen?”

Ms Patel responded: “Because legislation brought in by your government in 2008 meant that dangerous terrorists had to automatically be released after half of their jail term.

“Conservatives changed the law in 2012 to end your automatic release policy but Khan was convicted before this.”

Ms Cooper said there would need to be a “serious and full” investigation into how the incident happened given that the attacker was a convicted terrorist.

She told BBC News questions needed to be asked, particularly because there may be other people in the same situation as this attacker.

“There are deradicalisation programmes but there is a question about whether this attacker was a part of them, what the extent of them was, what the resourcing is behind them,” she said.

Sentences of Imprisonment for Public Protection (IPPs) were introduced in 2005 and given to violent or sexual offenders who posed a risk to society.

They would not include a fixed term of imprisonment but instead would give an offender a minimum period to serve before they could be released.

A prisoner serving an indeterminate sentence would stay in prison until it was found they were safe to be released, meaning they could remain locked up for decades if they were still thought to be dangerous.

They were abolished in December 2012, but only for new prisoners.

It’s thought Khan was automatically released thanks to the Criminal Justice Act – introduced by Labour in 2005 – which lets out prisoners halfway through their term, with the rest of their sentence under licence.