I know the rhetoric is more exciting and inflammatory, but the CPS view of Manslaughter is reasonably clear cut;
Homicide; Murder and Manslaughter: Legal Guidance: The Crown Prosecution Service
The Breach of the Duty of Care
The ordinary law of negligence applies to these cases, in that those with an established duty of care, must act as a "reasonable person would do in their position". If they fail to do so they will have breached that duty. This is an objective test and will be based upon the defendant's position at the time of the breach.
Therefore, if the defendant has acted within the range of what was generally accepted as being the standard practice (even if it is at the lower end) it will be difficult to describe such behaviour as falling far below the standard of a reasonable person in his position.
An unqualified person is not to be judged at a lower standard than a qualified person. Therefore the lack of skill will not be a defence if the conduct is deemed negligent. If however, the defendant has particular skills and knowledge of a danger that the reasonable person would not have, his actions should be judged in the light of those skills or knowledge. This test is an objective test.
It does not matter that the defendant did not appreciate the risk (the foreseeable risk of death) only that the risk would have been obvious to a reasonable person in the defendant's position. (R v DPP ex parte Jones 2000 CLR 858 and AG ref No: 2 of 1999 3 All ER 182.)
The Grossness of the Breach
It is for a jury to decide whether the defendant's conduct was so bad, in all the circumstances, as to amount to a criminal act or omission. In R v Misra and Srivastava [2005] 1 Cr App R 328, the court agreed with the direction by the judge that the term 'reprehensible' would be apt to describe the nature of the conduct.