Offenders should no longer be given sentences of under a year to ease the “enduring” prison safety crisis in England Wales, MPs have said in a damning report.

The justice secretary, David Gauke, is already looking at the possibility of scrapping jail terms of six months or less, with exceptions made for violent and sexual offences.

The move is backed in a report from the justice select committee, chaired by the Conservative MP Bob Neill.

Neill said: “Throwing money at the prison system to tackle multiple issues takes funding away from external rehabilitative programmes that could stem or reverse many of the problems.”

The report said: “We need a serious open public debate about the criminal justice system, the role of prison and its affordability. We are pleased that the justice secretary and prisons minister have acknowledged this but regardless of the political climate it cannot just be a long-term aspiration.

“There must be greater transparency so that everyone can understand the true costs and challenging nature of decisions which need to be made about public spending on prisons and other aspects of criminal justice.

“This should form the first step of the justice secretary’s ‘national conversation’. These issues cannot be hidden behind the prison gates any longer.”

The committee suggested the approach could go further, urging the government to “model” the effects of abolishing sentences of under 12 months in England and Wales.

Plans are already in place in Scotland to introduce a “presumption” against custodial terms of less than a year.

Gauke signalled a departure from the Tory “prison works” mantra as he revealed his vision for “smart justice” earlier this year.

Short custodial terms would be replaced by “robust” community orders under the blueprint.

A safety crisis has swept through much of the prisons estate in recent years, with assaults and self-harm at record levels. The committee warned it was a “grave and worsening” situation, which was unlikely to improve with the current prison population.

It said: “We are now in the depths of an enduring crisis in prison safety and decency that has lasted five years and is taking significant additional investment to rectify, further diverting funds from essential rehabilitative initiatives that could stem or reverse the predicted growth.”

Over the past 25 years, the prison population in England and Wales has almost doubled in size, the report said. At the end of last week, there were 82,417 people in jail.

The nature of the prison population is rapidly changing, with a higher proportion of offenders behind bars for serious violent or sexual crimes and an increase in the average age of inmates, the committee said.

The MPs called for a focus on services to reduce the £15bn annual cost of reoffending, and suggested ministers should consider whether judges could be given a role in monitoring those they sentence to community punishments.

The assessment also raised concerns that support given to 10 jails chosen for a £10m safety drive could be at the expense of others in “serious need”.

Th prisons minister, Rory Stewart, has pledged to resign if the scheme fails to achieve a reduction in violence and drugs at the selected establishments.