Ghurkas in JG. Malay police in khaki, except for some of their special service types. Head swaps or cutting back slouch hats to bush hats with various WW2 figures will give you the best match. Artizan's Australians are good candidates but TAG have useable 14th Army types, including Ghurkas. Perry 8th Army are good for conversions for Malay Police. I've done some myself. If you look at the Artizan 8th Army command pack there's an officer that's almost ideal as a British officer for the police.
Of coures all that disregards your stated intention to use WW1 figures and that there is a dedicated range by Brittania.