At its upper limit, the sentence available for manslaughter is not hugely different that of murder in reality as shown:
Manslaughter:
Life with a minimum term of 24 years before parole eligibility.
Murder:
Life with a minimum of 30 years before parole eligibility.
Both sentences above will be discounted for mitigating factors
There is a Whole Life Order (21 years of age and greater) but its use is relatively rare and even had they been convicted of murder and were over 21 years old at the time of the offence, the killing of PC Harper would be unlikely to attract this sentence.
Think of West, Bellfield, Shipman, Huntley, Brady and Hindley as examples of the crimes attracting whole life orders.
Cases that would normally fall into this category include:
- the murder of two or more people where each murder involves a substantial degree of premeditation/planning, abduction of the victim, or sexual or sadistic conduct
- the murder of a child involving the abduction of the child or sexual or sadistic motivation
- murder committed to advance a political/religious/racial/ideological cause;
- murder committed by a defendant with a previous conviction for murder.