The Commissioner of Police of the Metropolis is the force's administrative, executive and operational head. The posts of Commissioner, Deputy Commissioner, and Assistant Commissioner [the latter two not used in the Victorian era] all lie in the gift of the Crown (i.e. the appointments are made by the Sovereign on the recommendation of the HomeSecretary, to whom the Comissioner is responsible).
Fido, Martin, and Keith Skinner. The Official Encyclopedia of Scotland Yard. Rev. and updated ed. London: Virgin, 2000.