Boris Johnson has focused entirely on sentencing when discussing the implications of the terror attack at London Bridge – and in doing so ignores a wide range of factors that could have influenced the tragic outcome.

By concentrating on sentencing, the prime minister is able to focus on his opponents, Labour, for introducing the regimes under which the attacker, Usman Khan, was jailed. He can offer a quick fix: toughening up jail sentences is not difficult – governments can amend or introduce legislation and lock people up for longer with little challenge from wider society. It all fits neatly into Johnson’s tough approach to crime since taking up office.

Play Video 1:29 Boris Johnson blames Labour for early release of terror prisoners – video

But he is also deflecting from more complex issues that reflect poorly on his party’s record in government. Khan served time in prison and was released on licence at a time when the Ministry of Justice (MoJ) budget was slashed in real terms by 40%.

The impacts of these cuts are material. Inmates are spending up to 23 hours a day in the cells of understaffed and overcrowded prisons. The overhaul of the probation sector by Chris Grayling in 2014 is widely considered by inspectors, MPs, academics and probation workers to have been a disaster. Police forces, who would have been involved in Khan’s monitoring after release, also experienced a 20% funding cut.

It cannot have helped that there have been seven justice secretaries in nine years, unable to offer a consistent overview of policy at the embattled department.

In prison, work should have been taking place to rehabilitate Khan. The MoJ says he was enrolled on counter-radicalisation initiatives but his solicitor said none of these programmes tackled the underlying ideology and he ended up writing to organisations outside the prison requesting help.

Efforts by the government to tackle radicalisation in prison have been heavily criticised. Ian Acheson, a former prison governor who chaired a review of radicalisation in prisons, found it to be rife and made recommendations, which he says have not been implemented. One of his key recommendations was to segregate jihadist prisoners in specialist jails. But so far only a handful of prisoners have been placed in them, none of whom are engaging effectively with the work.

Once released, Khan was placed on a multi-agency public protection arrangement (Mappa), which would have involved probation, police and prison working together to manage him in the community.

Looking at the efficacy of the probation sector’s involvement, the impact of cost-cutting cannot be ignored. A report by the probation inspectorate on the Midlands division that would have been responsible for Khan, who was based in Staffordshire, found the service buckling under “substantial staff shortages” and workloads at 130% to 150% over capacity.

There remains the possibility that Khan was so duplicitous and his ideology so entrenched, that he was able to deceive probation and police officers in to believing he was low risk. But it could have been the case that the probation officers dealing with him were struggling with dozens of offenders on their books and the two meetings a week he was required to attend were cursory.

There have been reports of probation officers conducting checks over the phone, rather than face to face, and holding meetings in public spaces to discuss intimate issues with offenders. There is also the issue of levels of experience among probation officers. As in the prison service, the numbers of experienced officers has declined.

Johnson has launched a review of licensing conditions for all convicted terrorists released from prison but individuals subject to Mappa plans are already supposed to be reviewed once a month.

Harry Fletcher, the former head of the National Association of Probation Officers (Napo), has questioned why it took such a tragic event for these licences to be reviewed when a Mappa plan was in place and says resources must have been a factor. “Why has it taken this event for the review to take place? It still comes back to resources. I’ve heard cases where Mappa has been convened and there’s no police officer available to attend.”

Khan was compulsorily enrolled on the Home Office’s desistance and disengagement programme (DDP) but this is in its infancy and critics say has no evidence base.

Prior to Johnson taking office, the then justice secretary, David Gauke, was refocusing the approach of criminal justice to place rehabilitation at its core. Gauke was cautious not to apply this to the most serious offenders but it was indicative of a shift towards reducing reoffending through evidence-based policy. Similarly, in the Home Office, the then home secretary, Sajid Javid, had started to talk about knife crime as a public health issue, rather than a purely criminal one.

But under Johnson’s leadership, this way of thinking has dropped from the agenda and has been replaced by tough talk critics say is aimed purely and cynically at pulling in voters.

By shifting the conversation towards sentencing, Johnson is able to dodge tough questioning on the impact of austerity on police, prisons and probation, as well as the more complex issue of rehabilitation.