The majority of the nation's "hyper-prolific" offenders are being spared prison terms, according to a new report - despite having upwards of 45 previous convictions.
Hyper-prolific offenders were found guilty of almost 10,000 offences in 2022, but just 47% received jail time, data compiled by conservative thinktank Policy Exchange shows.
Prolific offenders - those with 16 or more previous convictions - were jailed even less frequently, with 24% being sent to prison for their next offence.
Researchers warned the state of the criminal justice system is a "public safety time bomb".
Prolific and hyper-prolific offenders make up only 9% of the 6 million people convicted of a crime between 2000 and 2021, but were responsible for half of the offences.
In one case, a prolific sex offender with more than 100 previous convictions, including indecently assaulting children, was given a suspended sentence after being found guilty of 15 charges involving indecent images of children.
In another, a man with 343 previous convictions received a community order and fine after being found guilty of 10 further theft offences.
The report, written by former Metropolitan Police detective chief inspector David Spencer, noted that even in the group of hyper-prolific offenders, "there are individuals who are redeemable".
But the criminal justice system is failing both them and the public, it said, with long waits to charge suspects and the backlog in the crown courts at a record high.
'Unacceptably high' reoffending rates
The prison population is growing but the report called conditions "a disgrace", with inmates rarely able to undertake educational activities that reduce the risk of reoffence.
"Reoffending rates of those leaving prison are unacceptably high, putting the public at huge risk," the report said.
The report called for two-year mandatory sentences for hyper-profilic offenders convicted of further crimes.
The report stated: "There are a group of offenders who are, despite their hyper-prolific offending which causes misery to the victims and communities, regularly avoiding prison sentences.
"It cannot be right or fair on the law-abiding public to have to tolerate this level of law-breaking by the same individuals time and again.
"Parliament must legislate so the courts sentence these individuals to prison when convicted. This would protect the public and provide the opportunity for these offenders to do the work that would lead them to being less likely to offend on release."
It also recommended a speedier progression of cases from charge to conviction and called for substantial prison reform.
MoJ says length of sentences has increased
A Ministry of Justice spokesperson said average custodial sentence lengths have increased by 48% over the last decade.
"While sentencing is a matter for independent judges, we have toughened up punishments for the worst offenders including ending the automatic halfway release for serious and violent criminals and ensuring their stricter management in the community to keep the public safe."
Last month, Justice Secretary Alex Chalk outlined plans to create extra prison space, including releasing some prisoners early and sparing low-level offenders jail altogether.