Hi Sue
Class Z Reserve was set up after the armistice. This allowed men to be discharged but with the understanding that they could be recalled if fighting started up again. 11 November 1918 was only an armistice. WW1 did not officially end with Germany until the signing of the treaty of Versailles in June 1919; and with Turkey not until 10 August 1920 under the Treaty of Sevres.
From 1914-1918.net:
Class Z Reserve was authorised by an Army Order of 3 December 1918. There were fears that Germany would not accept the terms of any peace treaty, and therefore the British Government decided it would be wise to be able to quickly recall trained men in the eventuality of the resumption of hostilities. Soldiers who were being demobilised, particularly those who had agreed to serve "for the duration", were at first posted to Class Z. They returned to civilian life but with an obligation to return if called upon. The Z Reserve was abolished on 31 March 1920.
Ken
