The Queen's Regulations and Orders for the Army. Part II. 1889
The Queen's Regulations and orders for the Army. 1895
The King's Regulations and Orders for the Army. 1904.
The 1904 Regulations ushered in fundamental changes regarding number sequences. Infantry regiments which had previously had to apply to start a new series once they were approaching 9,999 were now permitted to extend their numbering up to 19,999. (Nevertheless, the change in regulations came too late for some regiments which, having reached 9,999, had already started a new series from 1. I've mentioned these regiments in an earlier post on Regimental Numbering Series).
The Royal Artillery was now differentiated as  Royal Horse Artillery and Royal Field Artillery and  Royal Garrison Artillery, both numbering up to 49,999 as opposed to the 99,999 which had been used prior to 1904 for the Royal Artillery as a whole.
The 1904 Regulations also specifically mentioned the cavalry regiments (numbering up to 9,999).
Army Order 289 - December 1906
Army Order 289 changed the numbering as far as the cavalry of the line was concerned. (The regiments of Household Cavalry retained their regimental numbering sequences but were to only number up to 9,999). Prior to this Army Order there had been no numbering differentiation between Household and Line cavalry, and each individual regiment had maintained a separate numbering series. Now, the line cavalry was to re-number by the three corps: Dragoons, Hussars and Lancers.
I am unsure of the precise date when this Order came into effect. The lowest numbers currently on my line cavalry databases are 30 (Dragoon Guards on 9th January 1907), 15 (Hussars - 1st January 1907), and 104 (Lancers on 12th February 1907). Men already serving with the cavalry line regiments were not re-numbered and so one assumes that there must have been duplicate numbers in the three corps.
For example, before the Order came into effect, most of the line cavalry were numbering in the high 5000s, 6000s and even 7000s in some regiments (7th Dragoon Guards, 7th Hussars and 5th Lancers to give three examples of the latter).
With the change in numbering, the Dragoons had again reached 5000 by August 1910, the Hussars by December 1909 and the Lancers (which had always had fewer regiments) by December 1913. This also presents today's researchers with another conundrum. Does my line cavalry ancestor's number belong to the pre 1906 series or the post 1906 series? I'll deal with the individual cavalry regiments and the corps of cavalry in future posts.
The King's Regulations and Orders for the Army. 1908.
The 1908 Army Order extended the numbering series in the RHA and RFA to 99,999 whilst the RGA maintained the 49,999 limit which had first been indicated in the 1904 King's Regulations.
The King's Regulations and Orders for the Army. 1912. Amended up to 1st August 1914.
My grateful thanks to joseph of the Great War Forum for the copy of the 1889 Queen's Regulations, and to Graham Stewart for all the others. View British Army WW1 Records here.