Danny, your query re. discharge.
Other than those enlisted after the war began "for the duration", as a generality, soldiers on any engagement [regular of varying periods, TF, or Special Reserve] had a Termination of Engagement date which was to be extended by one year in case of war. This was enforced: "held to serve". Even in peacetime a soldier serving in far away places with strange sounding names could be held to serve if suitable transport and shipping was not available. Hence "Doolallytap!", a form of insanity allegedly brought on by being held at Deolali waiting for a ship to Blighty.
For soldiers discharged after their extra year of war there was a Catch 22. The Military Service Acts of 1916 allowed for them to be conscripted.
The Army whispered in the ears of those about to be shanghaied, offered a month's leave, a bounty and a retention of rank and regiment if desired.
If you need more, feel free to ask ......... its my Mastermind second subject. I forget what the first one is.