Nearly 4,000 criminals with more than 50 previous convictions were spared jail last year, new figures have shown, prompting MP calls for tighter sentencing rules.
The number of "super prolific offenders" who are convicted but not sent to prison has tripled over the past decade.
Roughly half of all crimes are now being committed by just 10 per cent of offenders, Ministry of Justice figures have shown.
Boris Johnson and Jeremy Hunt are under pressure to commit to supporting tougher sentences and boosting investment in prisons.
Since 2007, the number of offenders with more than 50 previous convictions who were convicted but spared jail has risen from 1,299 to 3,916 last year, according to data obtained through a series of Parliamentary Questions by Tory MP Neil O’Brien.
These included violent offenders - nearly a third of criminals convicted of violence against the person and had more than 25 previous convictions still escaped a jail sentence.
Meanwhile, early release of prisoners has risen sharply - one in five are now released without serving even half their sentence, up from 13 per cent in 2017.
Mr O’Brien said: “Large numbers of people should not be getting let out of prison before even the halfway mark of their sentence under early release.
“In the long run we should be moving to honesty in sentencing so people serve the time that is read out in court.”
The MP called for the next Prime Minister to review sentencing rules, including bringing back the ideas of minimum sentences and “earned release”.
Prisons need more investment to ensure they have the capacity to hold “super-prolific criminals” for longer, he said.
Mr O’Brien’s report for Onward, the think tank, also recommends toughening community sentences, suspended sentences and drug rehabilitation programmes. By the time offenders receive a jail sentence they have increasingly first served high numbers of suspended and community sentences.
One offender who was jailed last year had been previously given 47 community sentences in the past, according to the study.
Mr O’Brien said: “There is absolutely no contradiction between believing in more and better action to prevent crime, and tough sentences for those who commit a lot of crime. They should be two sides of the same coin.”
The MP, who is a government aide to the department for Business, Energy and Industrial Strategy, added: “There is much more that could be done to steer prolific offenders away from a life of crime at an early age. And one of the most important causes of prolific offending is drug addiction - for which we must improve treatment.
“But we must also protect the public from the small group of people who commit so much crime. Super-prolific offenders must face more certain and longer prison sentences.”
A spokesman for the Ministry of Justice said: “Sentences are decided by independent judges on the facts of each case and under this government the most serious offenders are more likely to go to prison and for longer.”