Thousands of prisoners have already been let loose midway through their sentences, with startling images of lags popping champagne and hopping in luxury cars making headlines last year.
Under the current schedule, two of PC Harper’s killers were due to have been let free just six years into their sentences.
The pair of killers, Albert Bower and Jessie Cole, were locked up for the manslaughter of PC Harper in 2019.
At the time, they had even been pictured laughing and acting up in front of the cameras as they entered court.
Bower and Cole were sent down for killing the 28-year-old police officer, who had been investigating the theft of a quad bike in August 2019.
They tried to flee the scene in a car driven by Henry Long when the officer was dragged more than a mile on country roads with his ankles caught in a tow rope.
It was revealed earlier this week that the pair could be released early, despite calls from the Conservative Party and campaigners to exempt killers, rapists and groomers from the scheme.
In a statement issued during a visit to Scotland, Mr Burnham announced that he would halt the September releases pending the outcome of a review.
The Prime Minister said: “Keeping the public safe will always be my top priority.
“I am working closely with the new Justice Secretary and have instructed my team to put a pause on the changes that were due to start in September.”
He added: “No prisoners will be let out under this policy until we have conducted an urgent review and done everything we can to minimise risk to the public.
“Where changes are needed, we will not hesitate to make them.”
Mr Burnham has been under sustained pressure from MPs, campaigners and PC Harper’s widow, Lissie Harper, to halt the release.
Before the announcement, Mrs Harper said it was “deplorable” that “releasing prisoners early is even considered acceptable”.
The national outcry at the officers’ killing resulted in Harper’s Law, which introduced mandatory life sentences for offenders who kill emergency workers while committing a crime.