Let's say that the Police Commissioner for a certain area lawfully delegates his conditional power to ban public processions to the Assistant Commissioner. This delegation is permitted under s15 of the Public Order Act.
If the Assistant uses one of these powers illegally to the detriment of Bob, he may be able to bring forward judicial review proceedings.
Will these proceedings be brought against the Commissioner (who delegated the decision) or the Assistant (who made the decision)?
The chief officer of a police force is answerable for the conduct of his constables (a category which includes even his immediate deputies).
This rule was originally formulated to deal with torts committed by constables, for which the chief constable would be vicariously liable. It is the same as the "master-servant" principle, but has a special status because the police are unlike ordinary employers. Constables are in some respects independent servants of the law in general (Fisher v Oldham Corporation [1930] 2 KB 364). The language from the Police Act 1964 s.48(1),
The chief officer of police for any police area shall be liable in respect of torts committed by constables under his direction and control in the performance or purported performance of their functions in like manner as a master is liable in respect of torts committed by his servants in the course of their employment, and accordingly shall in respect of any such tort be treated for all purposes as a joint tortfeasor.
was enacted in order to clarify and regularize the situation. This provision is now found in the Police Act 1996, s.88, where a recent amendment extended it not only to torts but "any unlawful conduct".
In the context of judicial review, rather than tort, it is the chief officer who by statute has "direction and control" of the force. That is in statute in the Police Reform and Social Responsibility Act 2011, s.2(3), and previously in other enactments (e.g. section 5(1) of the 1964 Act). A deputy or assistant chief constable, or the corresponding Metropolitan Police titles, does not have this special status. All judicial review instances that I've seen have named the Chief Constable rather than anybody else as the respondent.
The Extinction Rebellion case of R (Jones) v Commissioner of Police of the Metropolis [2019] EWHC 2957 (Admin) is not quite on target for this question, but in the same area. The judicial review was about policing of climate protests and the use of the Public Order Act. While there was no delegation of the kind referred to in the question, the JR was made against the Commissioner although the senior decision-makers actually involved were different people - a Superintendent, Chief Superintendent, and a Commander. (That last one is a unique MPC rank since they have more chief-type levels than other forces.) The Commissioner was not personally involved. The specific decisions being challenged were made by the Superintendent. Had an Assistant Commissioner also been in play, then it would still be the Commissioner who'd be named as respondent, as he carries ultimate responsibility for the actions of any of his officers.
In the same way, judicial reviews against the Crown Prosecution Service are phrased as R (Bob) v Director of Public Prosecutions, even when the DPP had nothing personally to do with Bob, but delegated matters to another prosecutor.
In U.S. law, most of the time, the courts treat all federal agencies, divisions, and personnel as a single person for purposes of litigation, with third-parties and does not allow litigation between them. The same approach is taken vis-à-vis state governments, and vis-à-vis particular local governments.
Agencies with delegated authority are generally sued separately only when they are corporations owned by the government (in whole or in part) with limited liability that protects the governmental owners (e.g. the Federal Deposit Insurance Corporation (FDIC)).
Sometimes individual government officials are named as defendants in public law litigation in their official capacity, in an action seeking a writ to judicially review a decision. This remains the norm in federal court practice.
In habeas corpus litigation, the nominal defendant is generally the warden of the jail or prison where the person seeking habeas corpus relief is detained in their official capacity. Some states, however, have departed from the traditional rule and treat what would be called a habeas corpus petition at common law, a post-trial motion in an original criminal cases when it seeks to collaterally attack a conviction.
In cases seeking to compel or prevent or review official action, in a mandamus or prohibition or certioari writ case, the nominal defendant is generally someone with the legal authority to take the action requested, or who actually took the action, in their official capacity.
But many states have replaced this approach with a special proceeding against the entity with the authority to act, discarding the legal fiction that the official sued in their official capacity is being sued. See, e.g., Colorado Rule of Civil Procedure 106 (Forms of Writs Abolished).
When a court order directed at an entity's behavior is ignored, the lowest level public official who is capable of complying with the order can be held in contempt of court.
Individual officials can also be sued personally for wrongdoing in which they personally participated while serving a government, either personally, or under color of law. When the wrongdoing is committed by a state or local official, the lawsuit is brought under 42 U.S.C. § 1983 if a federal right is violated. When the wrongdoing is committed by a federal official (in a narrow subset of violations of federal rights), the lawsuit is called a Bivens action.
In these cases, the personal participation of the official in the wrong doing determines who is a defendant, and there is no true vicarious liability. Everyone held liable must have some personal fault from their own actions. There is no vicarious liability and no concept of respondeat superior in these cases.
