The Metropolitan Police Act 1856 is an act of the Parliament of the United Kingdom, passed on 28 February 1856. The act modified the previous Metropolitan Police Act 1829 and Metropolitan Police Act 1839, merging the two roles of First Commissioner and Second Commissioner into the single role of Commissioner of Police of the Metropolis and setting up a system of two assistant commissioners under him. The roles of First and Second Joint Commissioner had been filled by Richard Mayne and William Hay until the latter's death in 1855. The act provided for one of the First and Second Commissioners to become the sole Commissioner as soon as the other one died – effectively it meant that no new Second Joint Commissioner was appointed and Mayne became sole Commissioner. The act also set the maximum for the Commissioner's annual salary at £1500 and that for each Assistant Commissioner at £800.