A couple of points of correction, Andy:
//...the CPS needs to prove beyond a reasonable doubt that the death of the victim was the accused's premeditated intention,...//]
There is no need to prove premeditation to support a murder conviction. Only "intent" is required and that intent can arise spontaneously.
//..and for a weight of evidence to provide a better than fity per cent chance of a conviction.//
The prospect of a conviction is not actually quantified. The Code for Crown Prosecutors simply says that there must be "...enough evidence to provide a 'realistic prospect of conviction' "
//In terms of manslaughter, as I understand it once again, a degree of intent has to be present,...//
The very essence of the difference between murder and manslaughter is that murder requires intent whereas manslaughter does not. Leaving aside "gross negligence" manslaughter, both murder and manslaughter must involve an unlawful and dangerous act. Again, quoting from the Code for Crown Prosecutors:
"The offence is made out if it is proved that the accused intentionally did an unlawful and dangerous act from which death inadvertently resulted."
So manslaughter can be seen, if you like, as "accidental murder."
//Looking at a siutation as a simple scenario, and deciding that an accused should be accused of something that will generate the maximum sentence, is not the way the law works.//
That is spot on, and a point often overlooked.