The Powels publication is not the source of the map. A prior source is the "A Brief Record of the Advance of The Egyptian Expeditionary Force", produced by the Government Press and Survey of Egypt, Cairo 1919. I have a copy.
As an official (British) government publication, I don't believe it is copyrighted.
The 1919 map does not have a copyright notice, it says "Printed by the Survey of Egypt, Dec 1918 (0453)".