Pay at the start of WW1 was covered by the 1914 Pay Warrant. I have a copy somewhere and will dig it out. It covers well over 1000 sections so the subject is not straight forward.
Deductions for wives and children were automatic at so much a day for the wife and so much for each child. There was I believe a maximum deduction of something like 8d a day. It probably changed during the war several times. When I have time I will confirm it. Deductions were automatic so that families were not dependant on the parish.
Regulars also had 1.5d a day allowance saved for them as a lump sum after 7 years. There was also efficiency/trade pay in a number of classes. Regulars also received good conduct pay at 1d a day each after 2, 7, 12(?) years etc.
Pay was however complicated by factors such as when a man enlisted. Two men getting the same class of efficiency pay could get different amounts, and could vary if they had experience in the Militia/Territorials. Hansard is full of questions from MPs informing parliament of cases that had been brought to their attention. One example:
Mr. BAKER The conditions under which service pay and proficiency pay are issued are laid down in Articles 1060 and following and in Appendix V. of the Royal Warrant for Pay of the Army, 1914. Service pay (Class I. 6d. to 7d. per day and Class II. 4d. to 5d. per day) is now being-drawn only in the case of men, serving with the Colours or in the Reserve on 4th August, 1914, who enlisted before 1st October, 1906, and have not since that date entered into a new contract by extension of service, re-engagement, transfer to another arm, etc. Such men draw this emolument, i.e., service pay, under the conditions in force at the time of their enlistment. Proficiency pay (Class I. 6d. per day, Class II. 3d. per day (is issuable to Cavalry, Artillery, and Infantry soldiers who enlisted on or after 1st October, 1906, or who, having enlisted before that date, have relinquished their service pay rights on entering on a new contract as stated above. A service qualification of two years Colour service is the only condition necessary during mobilisation for the Class II. rate (3d. per day) of proficiency pay (service on a prior engagement in the Regular Army, Royal Marines, Special Reserve, or, subject to certain conditions as to camp attendance, in the Territorial Force, may count for this qualification). To earn the Class I. rate (6d. a day) a private soldier must in addition have passed the standard test in shooting or be a qualified signaller. Non-commissioned officers of or above the rank of sergeant get Class I. rate provided they have two years' Colour service. All Reservists who have rejoined the Colours draw service or proficiency pay according to the class of service or proficiency pay they were drawing when they were transferred to the Reserve.
If men were paid the wrong amount the civil servants would try and recover the overspend as quickly as possible; leaving MPs to complain that men at the front had been left with a few pence a day for several months. Deductions for the families was always paid - although there were examples of payments being delayed by several months - to prevent families claiming parish relief etc.
Ken