Justice Secretary Alex Norris is drawing up plans to “maximise public safety and minimise the early release of prisoners”, Mr Burnham said.

It comes as the Prime Minister faces increasing pressure to prevent Pc Andrew Harper’s killers Albert Bowers and Jessie Cole from being freed early.

Prime Minister Andy Burnham (Image: Jack Taylor/PA Wire)

Mr Burnham pledged to do “everything possible” to ensure the pair aren’t eligible for early release.

Pressed on reports ministers are considering exempting prisoners who committed “unlawful act” manslaughter from the scheme, he said “at this moment in time, this is speculation”.

A former leading judge has warned it would be “unlawful” to block solely Bowers and Cole from early release while freeing other prisoners convicted of the same offence.

However, Lord Thomas of Cwmgiedd said the rule change surrounding the type of manslaughter could be workable in practice.

Bowers and Cole, two of the Abingdon-based cop’s three killers, were passengers in the car that dragged the police officer down a country road after he got caught in a strap attached to the vehicle as they fled the scene of a quad bike theft in Sulhamstead, Berkshire, in 2019.

Andrew Harper, who lived in Wallingford and was based at Abingdon police station. (Image: Thames Valley Police/PA Wire)

The prospect of the pair’s release next year halfway through their 13-year sentences has prompted widespread condemnation of the early release scheme.

Mr Burnham ordered a review of the scheme under the Sentencing Act shortly after taking office, but while changes were announced to prevent rapists and paedophiles being released early, the measures did not cover Pc Harper’s killers.

The Prime Minister told reporters: “I’ve said I want to do everything possible to ensure we don’t see the release of people involved in the killing of Pc Harper and other individuals.

“I recognise that it’s very hard for his family. The anniversary of his death passed just at the weekend, so we understand that this is a difficult time.

“But it is important, given the public concern, that I do everything possible to get this right. That I do everything possible to minimise early release. That’s why we’re looking at every way I can do that, with the Justice Secretary, and we’ll present our findings in two weeks’ time.”

Asked about the specific exemption, Mr Burnham said: “At this moment in time, this is speculation, because I asked the Justice Secretary to develop a plan to maximise public safety and minimise the early release of prisoners.”

Lord Thomas, an independent crossbench peer who previously served as lord chief justice of England and Wales, told BBC Radio 4’s Today programme: “People are found guilty of manslaughter in three different circumstances.

“One, because they’ve been charged with murder and have a specific defence.

“Secondly, because they have committed an act which is grossly negligent that has resulted in death.

“And thirdly, involuntary manslaughter…, where there’s been an unlawful act such as a punch, someone’s fallen over, hit his head on the kerb, and died.

“That is the unlawful act manslaughter which they’re seeking to exempt.

“So it is quite possible to distinguish the three types of manslaughter.”

Lord Thomas said “it may not be that straightforward” for prison staff to determine which type of manslaughter an inmate committed from their prison records.

But, he said, it “should be relatively easy to tell that from the sentencing remarks, which are always transmitted with the prisoner’s record”.

A Ministry of Justice spokesperson said: “Public safety will always be our priority.

“We are fast-tracking a plan to keep more of the most serious offenders behind bars, on top of murderers, anyone on life sentences and those in prison for rape, serious child sexual abuse and grooming offences who are already blocked from any changes.

“We share the public’s anger that these options are even being considered, after we inherited a prison system on the brink of collapse.

“We are fixing this by building 14,000 new prison places, expanding electronic tagging on an unprecedented scale, and investing in probation services at record levels.

“We are also exploring how we can go further, including faster deportation of foreign criminals, better use of the women’s estate and reviewing the unjust IPP (indeterminate sentence of imprisonment for public protection) sentences.”