I think they would need to be investigated in a similar way to medical manslaughter at a start, something that is concerned with actual fact finding.
Experts and Process
In all cases of medical manslaughter, the evidence of medical expert/s will be required. There will most usually be a pathologist report and expert evidence will be required concerning whether the actions or omissions of the medical professional caused the victim's death.
If causation can be proved, medical evidence will be needed to provide an opinion on how far below the standard of the reasonable medical professional the conduct fell. Sometimes the advice of several experts is required on different aspects of the case.
While considerable weight will be attached to the expert evidence, which will inform and assist the making of the decision in any case, the decision as to prosecution and whether the evidential test is met is ultimately one for the independent prosecutor.
Experts are required to have suitable and relevant expertise in their area of practice and will make a declaration as to their independence and expertise when they provide their reports.
The prosecutor will provide terms of reference for the expert outlining the elements of the offence of GNM and will address any aspects of the individual case that require particular expert advice.
In a case where the prosecutor considers that the evidence indicates that the threshold for a prosecution of GNM may be reached, senior counsel will be instructed to advise.
In cases where a charging decision of GNM is under consideration, the prosecutor and counsel will meet with the expert/s to discuss the report/s and the evidential test for GNM. Notes will be taken of any such meeting and any information which meets the disclosure test will be provided to the defence if a prosecution is commenced.
All review decisions in cases of gross negligence manslaughter are made by specialist prosecutors or senior specialist prosecutors in Special Crime Division and require the approval of the Head of the relevant Unit and final authorisation by the Deputy Head of Division.
https://www.cps.gov.uk/legal-guidance/gross-negligence-manslaughter