Every person enrolled under this Act shall be entitled to receive his discharge from the Territorial Army on the expiration of the period for which he was enrolled and any such person may, prior to the expiration of that period, be discharged from the said army by such authority and subject to such conditions as may be prescribed:
     Provided that no enrolled person who is for the time being engaged in military service under the provisions of this Act, shall be entitled to receive his discharge before the termination of such service.