I'm not quite sure why you are linking the RAIB▸ to prosecutions. They don't apportion blame, nor say yay or nay to prosecutions.
Where's there's a suspicion that someone was at fault to the extent of criminality, it's right that the relevant bodies (Police, Health & Safety Executive, Crown Prosecution Service) investigate and, if necessary, charge.
Those investigations are needed to ensure public confidence. The Merseyside incident resulted in a guilty verdict. Hayes incident, not guilty. Both correct verdicts based on all the evidence.
What has trust between union and TOC▸ got to do with investigating possible criminal acts?
Agreed. The RAIB, like the
AAIB▸ , is there to examine the evidence of an accident, to the end of helping to make sure that no-one else makes the same mistake. Names are not mentioned, although "driver/pilot" is an obvious pointer. The law enforcement agencies examine much the same evidence to the end establishing if any laws were broken, and if so, by whom, to enable the Crown Prosecution Service to press charges against wrongdoers. I am not aware of any case where evidence gathered or opinions expressed by an investigating branch has been presented as evidence in a criminal prosecution.
Of course, the same evidence will often be gathered by the two different investigatory agencies, but the interpretation of that is different. Suppose an accident occurs whilst a driver is opening a chocolate bar. The evidence is clear, as a video recording shows the driver diverting his gaze from the window to the recalcitrant wrapper.
The RAIB find that the accident happened because the driver's attention was diverted, and recommends that TOCs issue rules to forbid the opening of food packaging while controlling a moving train.
BTP▸ find that the accident happened because the driver's attention was diverted, and consider whether this constitutes a criminal action or omission in breach of any law.
Trust between unions and TOCs is not an issue in either case. The union may support the driver in any negotiations as to his continued employment, and/or provide legal assistance.