Absolutely not!
If you were the family of the policeman, wouldn't you want to ensure that if found guilty, the killer was brought to justice in a British jali?
If you commit a crime in the UK, you should be tried here and serve your sentence here. Same as those British backpackers who 'accidentally' smuggle heroin into Malaysia.
Incidentally, I wouldn't instantly assume someone is subhuman because they're a murderer. Maybe of they were a cannibal (like that German fella a couple of years ago), but not simply for being a murderer.
Let me put it to you - if someone you knew had been murdered, wouldn't you feel a twinge of injustice if they were sent packing to spend time in a foreign jail, not knowing whether or not the local laws would set them free in a couple of years?
We don't even know whether this fella was from a 'friendly' nation.
Nah. You commit the crime here, you do the time here. Simple as that.
Once the time is served, he can be processed by the immigration and naturalisation services as normal, and that's when he should be deported.