Criminals who are "bang to rights" will no longer be given discounted prison sentences if they plead guilty under proposals being considered by the Government, The Telegraph understands.
Robert Buckland, the Justice Secretary, is studying plans to end the current practice of automatically giving convicted criminals one third off their sentences if they plead guilty the first time they are asked in court.
The move comes amid a public outcry after one of the teenage killers of PC Andrew Harper had his sentence reduced by eight years to 16 because of his guilty plea to manslaughter and his age.
Ministers fear the third off rule may be undermining confidence in the criminal justice system and is being exploited by offenders who were caught in the act but know they can reduce their sentence by one third by pleading guilty.
"If you get caught red-handed killing someone, say on camera, should you really get a third off for pleading guilty?" said a source.
"The rule is designed to help victims so they don't have to go through the stress of giving evidence. What it is not supposed to be is for criminals to exploit it by seeing they are 'bang to rights' and then game the system for their own benefit.
"That's where it is open to exploitation for the wrong reasons. It's then benefiting the criminals rather than the victims."
It is understood the policy is likely to be initially focused on murder and manslaughter but could be extended to other serious offences. It was being considered before the sentencing of PC Harper's killers.
The rules, introduced in 2016, give judges a sliding scale starting with a third off, followed by one fifth if the criminal pleads guilty later but before the first day of the trial and one tenth if they change their plea on the first day. It is a zero reduction for any time later.
Henry Long, 19, the driver of the car that dragged PC Harper to his death, denied murder but admitted manslaughter, earning him the eight-year discount and entitling him to a potential release on parole in 10 years and eight months.
PC Harper’s widows, Lissie, launched a campaign on Wednesday for automatic life sentences for killers of emergency service workers, saying the three teenagers' jail terms were inadequate for criminals who had brought such "utter despair and grief" to her life.
Sir Mike Penning, a former policing and justice minister, said it was "perverse justice" to let a criminal get one third off simply for pleading guilty when they were caught red-handed.
"The liberal brigade will go mad about this because it will fill up prisons, but the victim should be put in the driving seat for once," he said.
Caroline Shearer, who set up an anti-knife crime charity after her son Jay was stabbed to death, said: "If I pleaded guilty to not paying my electricity bill, should that mean I get a third off it?
"It is not teaching these people. They need to be put on solid, mandatory tariffs. If you get X years, you should do X years."
Her son's killer was jailed for 17 years but the youth who admitted his role in the affray that led to his death got only two years. After his release, he was subsequently jailed for 16 months after being caught with a knife in a stolen car.
The Criminal Bar Association (CBA) and Bar Council, however, warned that the change could have the opposite effect by encouraging "bang to rights" offenders to take their chances with a jury.
"My experience is that if you don't give a defendant an incentive to plead guilty, they will fight on the basis that a jury might actually take sympathy and feel sorry for them," said James Mulholland, the CBA's vice-chair.
Asked about the plans, a Government spokesman said: "No comment."