However in general you should always be allowed to know who is making a complaint against you. If in this case you had not been wearing the headcam, the manager may have still taken your complaint on board, but the driver has a right to know who you are; you could be best pals of a workmate that has a reason to get you into trouble.
In Scotland, as far as the polis is concerned, you have a right to know who is making a complaint agaist you.
You are right that these are different circumstances from the case in question. However, it is interesting to explore them a little.
In the police example, I think it is important to distinguish between civil cases and criminal cases. (I know the law differs in Scotland compared to England, but I suspect the principles may be similar.) Also, I am not a lawyer, so this is just my understanding of the position.
In both civil and criminal cases, the court is acting as an arbiter between two parties.
In a civil case, it is Person A vs Person B, so it is usually necessary for a defendant to know who their accusers are. If Person A wishes to remain anonymous, then they have the choice of simply not pursuing the case.
In a criminal case, it is The Crown vs Person B, and Person A is simply a provider of evidence. In some cases, that evidence may be eye-witness testimony, so it is necessary for Person A to appear in court, but usually they are not obliged to testify. If they don't testify, it may mean that the case collapses, but it is still the choice of the witness. (In extreme cases, a witness may be required to testify, but that is exceptional.)
In the company disciplinary case, the manager is not acting as an arbiter between two parties at all. It is The Company vs their employee (Person B). They are investigating a company disciplinary case, and Person A is simply a provider of information. The company is required to act "reasonably", so they should only use the evidence that is available and not supposition. However, there is no obligation on the company to reveal the source of their information. If the value of the information is dependent on knowing the source, then there is a need for those involved in the disciplinary case to be aware of that, otherwise the information cannot reasonably be used, but that doesn't include Person B. The bottom line here is that the accuser of Person B is their company, not Person A, so the identity of Person A is irrelevant to Person B.
