During the Hundred Years War era, noblemen captured in a battle were normally held for ransom. In such a case, who got to keep the prisoner, provide him lodgings, and receive the ransom? Was it the soldiers who captured him? The lord which the soldiers served? Or the sovereign which the lord served?
A prisoner captured in battle belongs to the "state" of the soldiers who captured him. In theory, that would be the king of England or France.
Now it is possible that with at least some high ranking nobles, the king of England or France would let the capturer keep the prisoner. But this would be a form of "delegation," not a usual practice.
But common soldiers wouldn't keep the prisoner. They'd hand him up the "chain of command" to an officer, their lord, and ultimately the king.