Thousands of serial offenders with more than 50 previous convictions were spared jail last year, according to a new report which calls for a review of sentencing.
Centre-right think tank Onward found the number of "super-prolific" criminals in England and Wales who were convicted but not sent to prison tripled from 1,299 in 2007 to 3,916 in 2018.
The report - written by Tory MP Neil O'Brien - calls for prolific offenders to be jailed and to receive longer sentences, and recommends a review of sentencing of prolific offenders.
Mr O'Brien said: "Whoever is the next Prime Minister must invest in our jails and ensure that super-prolific criminals start getting the time in prison they deserve.
"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."
He said there was "absolutely no contradiction between believing in more and better action to prevent crime, and tough sentences for those who commit a lot of crime", adding: "They should be two sides of the same coin.
"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."
- Press Association