Modern Usage By Country: (6) United Kingdom and the Commonwealth: See also: Special Constable and War Reserve Constable. Within the British Police, Constable is the starting rank in all police forces. All police officers hold the office of a constable. Upon being sworn in, each officer starts at the rank of constable and is required to undergo a two-year probationary period. Upon successful completion, constables can remain at their current rank, specialise in criminal investigations, or apply for promotion to sergeant, the first supervisory rank. Constables wear an epaulette attached to the uniform, displaying their personal identification number. Within Greater London's Metropolitan Police, all constables and sergeants display a divisional call sign, as well as an individual number. The rank of detective constable (DC) is not senior to that of a uniformed constable, the 'detective' prefix identifies the officer as being part of CID or other investigative unit. A new probationary constable within a county police force is paid an annual salary of £23,259, with this rising to £25,962 after training, reaching a ceiling level of £36,519. Constables within the Metropolitan Police Service are paid an additional London weighting allowance which is currently set at £2,277. Head constable is the title for a police sergeant in some Commonwealth police forces. It was also previously the title for a head of a police force, until it was changed tochief constable