The terrorist behind the Streatham attack had reportedly told fellow inmates in jail that he wanted to murder an MP and mocked up an Islamic State-style execution.

Sudesh Amman, 20, was released from Belmarsh prison just days before he was shot dead by police during a knife attack in Streatham High Road on Sunday.

Amman, who was wearing a fake bomb vest during the violent knife spree, had voiced his intentions to “take out” MPs, a former prisoner who spent time with him told The Times.

The source told the newspaper that the terrorist wanted to copy the murder of Labour MP Jo Cox and had said: “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”.

Streatham terror attack - In pictures 21 show all Streatham terror attack - In pictures 1/21 Police are dealing with an incident in Streatham Andy Bullemor 2/21 Police officers conduct a search of a bail hostel in south London AFP via Getty Images 3/21 A woman reacts near to the scene where a man was shot and killed by armed police Getty Images 4/21 Forensic officers at the scene following the terror attack in Streatham High Road PA 5/21 Police cordon off a property in Streatham PA 6/21 Forensic officers outside a property on Leigham Court Road, Streatham PA 7/21 Police activity at the scene following the terror attack in Streatham High Road PA 8/21 Police officers look under a bus as they work at the scene of Sunday's terror stabbing attack in the Streatham area of south London AP 9/21 Forensics investigate the scene of the terror attack on Monday morning Jeremy Selwyn 10/21 Armed police at the scene in Streatham High Road PA 11/21 Police officers at the scene after a man was shot by armed police Getty Images 12/21 Forensics investigate the scene of the terror attack on Monday morning Jeremy Selwyn 13/21 Armed police officer on Streatham High Road PA 14/21 Forensics investigate the scene of the terror attack on Monday morning Jeremy Selwyn 15/21 Police officers guard a cordon on Streatham High Road, at the junction of Prentis Road AFP via Getty Images 16/21 Forensics investigate the scene Nigel Howard 17/21 Police officers at the scene after a man was shot by armed police Getty Images 18/21 Armed police at the scene in Streatham High Road PA 19/21 Items left on the pavement at the scene in Streatham High Road PA 20/21 Police secure the area in Streatham AP 21/21 Forensics investigate the scene Nigel Howard 1/21 Police are dealing with an incident in Streatham Andy Bullemor 2/21 Police officers conduct a search of a bail hostel in south London AFP via Getty Images 3/21 A woman reacts near to the scene where a man was shot and killed by armed police Getty Images 4/21 Forensic officers at the scene following the terror attack in Streatham High Road PA 5/21 Police cordon off a property in Streatham PA 6/21 Forensic officers outside a property on Leigham Court Road, Streatham PA 7/21 Police activity at the scene following the terror attack in Streatham High Road PA 8/21 Police officers look under a bus as they work at the scene of Sunday's terror stabbing attack in the Streatham area of south London AP 9/21 Forensics investigate the scene of the terror attack on Monday morning Jeremy Selwyn 10/21 Armed police at the scene in Streatham High Road PA 11/21 Police officers at the scene after a man was shot by armed police Getty Images 12/21 Forensics investigate the scene of the terror attack on Monday morning Jeremy Selwyn 13/21 Armed police officer on Streatham High Road PA 14/21 Forensics investigate the scene of the terror attack on Monday morning Jeremy Selwyn 15/21 Police officers guard a cordon on Streatham High Road, at the junction of Prentis Road AFP via Getty Images 16/21 Forensics investigate the scene Nigel Howard 17/21 Police officers at the scene after a man was shot by armed police Getty Images 18/21 Armed police at the scene in Streatham High Road PA 19/21 Items left on the pavement at the scene in Streatham High Road PA 20/21 Police secure the area in Streatham AP 21/21 Forensics investigate the scene Nigel Howard

Amman was released from prison on January 23 this year after serving half his three year and four-month sentence for possessing and distributing terrorist documents.

The government has announced plans to introduce emergency legislation to prevent terrorists from being released automatically after serving half of their sentences.

Justice Secretary Robert Buckland addressed the House of Commons on Monday afternoon following a terrorist attack.

Justice Buckland told MPs: “Yesterday’s appalling incident makes the case plainly for immediate action.

“We cannot have the situation, as we saw tragically in yesterday’s case, where an offender – a known risk to innocent members of the public – is released early by automatic process of law without any oversight by the Parole Board.

“We will be doing everything we can to protect the public, that is our primary duty.

“We will, therefore, introduce emergency legislation to ensure an end to terrorist offenders getting released automatically having served half of their sentence with no check or review.”

Sunday’s knife rampage led to three members of the public being hospitalised, although none are in a life-threatening condition.

Amman was under active surveillance since his release because authorities were concerned he still held extremist views.

Legal experts raised concerns about plans to apply the new rules to prisoners who have already been sentenced, with former independent reviewer of terrorism legislation Lord Carlile telling BBC2's Newsnight: "I think it may have gone too far.

"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."

Scotland Yard said armed officers were following Amman on foot as part of a "proactive counter-terrorism surveillance operation" when the incident took place.

The three victims were taken by ambulance to south London hospitals.

One man, in his 40s, is in a serious but stable condition, police said.

A woman in her 50s, a teacher at a nearby school, had non-life threatening injuries and has been discharged from hospital.

Police said a second woman, in her 20s, who suffered minor injuries believed to have been caused by glass following the discharge of a police firearm, has also left hospital.

Investigations continue with officers also searching two addresses in south London and Bishop's Stortford, Hertfordshire.

The attack in the south-London suburb comes just over two months since the London Bridge attack when two died and others were injured at the hands of Usman Khan a recently released convict who had been released on licence after serving time for terrorist offences.

He too had worn a fake suicide vest and attacked unsuspecting members of the public with a knife. He was also shot dead by armed police.

Both incidents have led to a spotlight being put on the current criminal justice system, with many calling for longer sentences while others urge for better rehabilitation.

Those killed in the London Bridge attack, Jack Merritt and Saskia Jones, were both working at the time for Cambridge University's Learning Together prison-rehabilitation programme and Merritt's father spoke out publicly against Prime Minister Boris Johnson's promise to introduce harsher punishments.

The bridge attack prompted a raft of measures to be proposed including forcing dangerous terrorists who receive extended determinate sentences to serve the whole time behind bars.

Following the most recent attack, Mr Buckland said the government would be looking to change legislation with "the underlying principle has to be that offenders will no longer be released early automatically and that any release before the end of their sentence will be dependent on risk assessment by the Parole Board."

“We face an unprecedented situation of severe gravity and, as such, it demands that the Government responds immediately and that this legislation will therefore also apply to serving prisoners," he added.

“The earliest point at which the offenders will now be considered for release will be once they have served two-thirds of their sentence and, crucially, we will introduce a requirement that no terrorist offender will be released before the end of their full custodial term unless the Parole Board agrees.

“We will ensure the functions of the Parole Board are strengthened to deal even more effectively with the specific risk that terrorists pose to public safety so, for example, we will ensure that the appropriate specialisms are in place.

“That work is in train and we will take steps to implement this as soon as possible.”

The Cabinet minister said "robust safeguards" should be put in place when a terrorist offender is released.