The Air Ministry was** the political government department responsible for the high level direction of the RAF. Staffed by civil servants and service personnel. In such departments, messengers were the men and women who, in the pre email days, moved files and records about from one office to another.
He would have had a civil service record but I am uncertain as to whether they were retained and are accessible.
MaxD
** Was because with the War Office and the Admiralty, there is now just the one Ministry of Defence.