Yesterday’s would-be Jihadi attack in Streatham should be seen in a wider context, to understand what it tells us about terrorism and specialist policing in the UK.

It is clear that the combination of anti-terror surveillance by the Security Service and specialist, armed counter-terrorism policing have become extremely effective in quickly neutralising armed attacks. Lessons were learned in the wake of the tragic shooting of the innocent Jean Charles de Menezes in 2006. Since then, sophisticated protocol and specialist counter-terrorist firearms teams have been established, to considerable success as yesterday’s events illustrate. Sudesh Amman was shot within minutes of first brandishing a knife, sadly not quickly enough to prevent him stabbing two bystanders.

The style of his attack was clearly inspired by Usman Khan’s rampage on London Bridge in November last year, which also involved the use of a fake suicide vest. Both attacks illustrate the successes and failures of current counter-terrorism strategy. Since the relative professionalism of the July 7 2005 London bombings, sophisticated, organised terrorism, with the use of professional or improvised explosives, has become much harder to perpetrate.

The 2017 bombing at the Ariana Grande concert in Manchester, although catastrophic, was less sophisticated than its predecessors. Terrorism now mainly appears to be isolated events inspired, rather than organised, by international terror groups and crucially without the use of explosives. The bigger picture is of revolutionary success in counter-terrorism operations.

Of course, the “Lone Wolf” phenomenon is much harder to prevent, as there is little or no intelligence or planning activity for the security services to intercept, and which can give some sort of warning. Despite this, the number of annual terrorist events has decreased markedly since peaking at 137 separate incidents in 2013. That figure has dropped to single digits in the last two years. Although the years from 2013 to 2017 were marked by hundreds of annual incidents, that figure and the actual number of casualties pale into insignificance compared to the height of the IRA’s campaign from the mid-70s into the ’80s and ’90s.

The fact that police were able to neutralise Amman so quickly was because he was under surveillance by armed police, a decision which would have been authorised only because he was considered a high risk in the first place. The question is why he was on the streets and able to commit an attack just days after being released on parole, having served only half a previous terrorism-related sentence.

The failure is partly explained by overly lenient sentencing for non-violent terrorist offences, but is mostly that of the probation system. This was also the problem that led to Usman Khan’s early release and insufficient vetting of his movements. In this latest incident, the disparity between early release and the fact that Amman was under surveillance by armed police from the moment of release, highlight a perverse disparity with specialist counter-terrorist police now effectively filling a public order void.

After the London Bridge attack, Boris Johnson made a manifesto pledge to revisit the issue of early parole in the case of violent offenders. That should now be revisited and expanded to include all those convicted of terrorism offences. In both cases, the terrorists were previous offenders, long past the point at which the government’s deradicalisation programmes could have offered a useful intervention.

There is a separate question about making sure that time in prison serves to prevent further radicalisation. At the end of last year a former prison governor, Ian Acheson, wrote in detail about the amateurish, in-house nature of deradicalisation in Britain’s prisons. This is an issue that demands serious attention by government. But, in the first instance, the government need to make sure that in the case of terrorist offences, violent and otherwise, that full sentences are served.

With only a gap of a few months between the last two terror attacks, the government needs to make some quick decisions about how to deal with the 220 or so people who were deemed to represent a similar level of threat to Khan, at the end of the last year. Some of them may well have been paroled or be coming up for imminent parole.

While from a policing perspective this number is manageable, it is notable that the security services only have the capability to mount in the region of 500 concurrent surveillance operations. The government must take action in order to prevent another Khan or Amman being released onto our streets. Only then can a more serious rethink of counter-radicalisation start to address the root causes.