In 1946, having failed his attempt to be elected to parliament, Fergusson returned to Palestine during the Palestine Emergency in the rank of a brigadier, and was appointed to several positions in British Mandate of Palestine police and para-military forces. At first he served as the commander of the "Police Mobile Force", a police unit of 2,000 British soldiers, that was used as a strike force against the Jewish insurrection. By the end of 1946 the unit was disbanded, by the order of the Palestine Police commandant, Col. William Nicol Gray. Fergusson was appointed as the commander of a police school that was supposed to be created in Jenin, but soon he was appointed by Gray to be "Special assistant to the commandant of police".