I have had a look at the CLA rules and they seem ok for skirmishes but as I am thinking of gaming the larger engagements I will need rules that can work on the batallion or brigade level.
From the Don Featherstone rules:
"These rules are compiled to govern a World War 1 Colonial Campaign - in German South-West Africa. The troops concerned are white European and Colonial infantry including Naval Landing Parties and cavalry; together with native infantry and cavalry. They are aided by light horse artillery and machine-guns; tractor-drawn field guns; "boiler-plate" solid-tyred armoured cars and light tanks. The infantry regiments are 20 men and 2 officers; the cavalry are 1 officer and 14 men."
You would need to remember these rules date back to the mid 1960s. If you think they might be what you're after I understand they have been reprinted by John Curry in Don Featherstone's Lost Tales.