I think one important aspect which you have somewhat overlooked, Gromit, is that, as far as I know, none of the 333 people slain by murdering police officers in the UK was in jail, under sentence of death, for blasphemy. Nor, as far as I know, were any of them shot whilst they were incarcerated.
Furthermore, the report that the Guardian article refers to says that prosecutions were recommended in just 13 cases (3.9%) suggesting that in more than 96% of the cases police officers were not held to blame for the deaths. In those cases files for prosecution were prepared based on "relatively strong evidence of misconduct or neglect".
"It is clear to us there is some real difficulty in this area." Said IPCC chair Len Jackson. “The IPCC had a responsibility to investigate and present a file to the CPS if we feel there are any matters potentially of a criminal nature", he said. But then it was up to the criminal justice system. "We have a jury system that is as good as anything in the world, but it is clear that juries quite often find it difficult to convict police officers."
Methinks Mr. Jackson jumps to conclusions for what is clear to me is that juries quite often find it difficult to convict anybody of murder – police officer or not – unless robust, clear and incontrovertible evidence is available. Alas “relatively strong” evidence is usually not enough and to be unlucky with a jury on 13 occasions defies the odds.
A brief shufty at the causes of these deaths is also interesting. I’m sure the report would mention specifically if any had been shot. Since it does not I stand by my comment in my first paragraph. The majority were from natural causes, with nearly three-quarters relating to drug or alcohol abuse, so that rules out about 250. Out of the total of 333 deaths, 87 people had been restrained, most commonly being physically held down by officers. Easy to say that officers should be careful when handling raving drug-addled maniacs in the confines of a police cell. You should give it a go.
I don’t think your comparison stands up to much objective scrutiny.