Perhaps I didn't explain my views adequately . . .
The Courts already have all the powers they need. The maximum sentence for manslaughter is the same as for murder, a life sentence. And in cases of murder they can also impose whole-life sentences, I think that about 36 people have been sentenced to this.
Harry Roberts is an example of how the law works.. He served 48 years for murdering 3 police officers and wasn't released until he was 78, by which time he probably wasn't a threat to anyone else.
Judges don't always get it right, and if the Attorney General thinks that they've been too lenient then there's a process that can put things right, which is being followed in this case.
Your proposal is for a mandatory life sentence for anyone who kills or seriously injures a police officer, and this wouldn't work for two main reasons:
1. Judges need to be able to exercise discretion and take the circumstances into account, that's why we have them.
2. When people face a mandatory life sentence they have nothing to lose, and would likely lead to much greater violence.