Our statute books are littered with examples of bad laws enacted in knee-jerk reactions to major terror attacks against London.

Judging by Boris Johnson’s comments yesterday about the need for harsher sentences and delayed release dates for terrorists, it seems the knife attack on London Bridge will be added to that list.

Speaking immediately after the incident, Johnson said it was a “mistake to allow serious and violent criminals to come out of prison early and it is very important that we get out of that habit and that we enforce the appropriate sentences for dangerous criminals, especially for terrorists, that I think the public will want to see”.

But such electioneering does not help answer the much more serious questions underlying the problems faced by the security services who have the job of keeping us safe.

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

Usman Khan, 28, who had been released from an eight-year prison sentence last year for his part in a plot to blow up the London Stock Exchange, went on a knife rampage killing two people and seriously injuring three others.

He was shot dead by police minutes later after being brought to the ground by members of the public.

The nature of the attack was all too familiar to Londoners and tourists to the capital who were the victims of terror knife attacks on Westminster Bridge and London Bridge in 2017.

Johnson’s inevitable call for tougher prison sentences and restricted probation for terrorists will not end these attacks. A few more years behind bars will not stop a radicalised and determined offender from leaving prison and carrying out an attack, it only postpones it.

If Boris Johnson is serious about eradicating the reoffending risk posed by convicted terrorists then he will have to enact laws to make sure all terror offences, no matter how serious, attract life sentences without parole.

But we live in a liberal democracy that supports a criminal justice system where the sentence matches the crime. If criminal law is to continue to enjoy the trust and confidence of the people then sentencing policy must be just and proportionate. Only totalitarian regimes, like North Korea and Bashir al-Assad’s Syria, use disproportionate sentences to lock away enemies of the state for life without any hope of release.

Yet the state does possess means to mitigate the risk of a prisoner reoffending. One is by beefing up our police and security services so the streets are properly patrolled and we have sufficient intelligence officers to assess the risk posed by individuals living in our communities. The other is to make sure prisons provide adequate rehabilitation services and that there are enough probation officers to help an offender safely return to society.

But in the past nine years police officer numbers have been reduced and rehabilitation and probation services have been cut to the bone.

While more beat officers may not have been able to stop Friday’s attack, counterterrorism teams who monitor terrorists released from prison play a vital role in evaluating their risk.

Damaging reforms to the probation service introduced in 2014 have led to probation officers complaining that they are no longer able to properly supervise dangerous offenders.

Experts, including the chief inspector of probation, have long feared that confusion caused by a lack of clear responsibility for those on probation will lead to dangerous offenders falling between two stools.

In 2012, Khan was sentenced to an indeterminate detention for “public protection” with a minimum jail term of eight years. This sentence would have allowed him to be kept in prison beyond the minimum term.

The same year the coalition government abolished these kind of sentences. In 2013, Khan successfully appealed his sentence and it was replaced by a 16-year fixed term which meant he was liable for release in December last year.

At the time, Lord Justice Leveson said: “There is an argument for concluding that anyone convicted of such an offence should be incentivised to demonstrate that he can safely be released; such a decision is then better left to the Parole Board for consideration proximate in time to the date when release becomes possible.”

All this shows is that the law cannot hold terrorists like Khan forever. But he was well known to the police and MI5 and upon his release his name would have been added to a growing list of individuals who need monitoring.

Support free-thinking journalism and attend Independent events

Scotland Yard’s counterterrorism command, MI5 and GCHQ share a database of 23,000 subjects of interest. Of these, they have prioritised 3,000 who they believe pose the greatest threat. Under MI5’s traffic-light system, a further 500 are given the highest priority and are being investigated as part of ongoing counterterrorism operations.

But the hardest cases to stop are the kind witnessed on Friday, involving lone-wolf attacks with little planning. Since the 9/11 terror attacks in 2001, 500 terrorists have been freed in the UK. The conflict in Syria has greatly added to this number so that last year a convicted terrorist was being released onto the streets of Britain nearly every week.

It is impossible to police the mind of every freed terrorist.

The sad truth is that the evil committed by convicted terrorists like Usman Khan is the terrible price we pay for living in a free democracy.