(1) A vacancy in a Prisons Service post or rank may be filled-

(a) by promotion, that is by appointing a prison officer who is to be moved from another grade or rank with an immediate increase in his salary;

(b) by transfer within the Service, that is by appointing a prison officer who is to be moved from another grade or rank with no alteration in his salary;

(c) on reduction in rank, that is by appointing a prison officer who is to be moved from another grade or rank with an immediate reduction in his salary;

(d) by recruitment, that is by appointing a person who is not a prison officer or who would cease to be a prison officer if the appointment were not made.

(2) Wherever practicable, a vacancy in the Prisons Service shall be filled either by promotion or transfer within the Service.

(3) Promotions shall be made according to merit.