Definitely British related in style, in the sense of British Colonial forces.
Tropical/warm climate Khaki drill material.
The pleated breast pockets and their design are very typically WW2 era British and Colonial forces in style, and also 1930's and post WW2 era.
The hat looks typically Australian slouch hat, although they usually had a cloth band around the hat, but perhaps the tonal contrast in the photograph doesn't allow the hatband to show.
The chevrons with the crown above them is Staff Sergeant rank, also typically British/British Colonial in design.
I think, probably Australian Army WW2 or post WW2 (1950's) era.
I suggest that you try a post on a more specialised uniform forum with an Australian sub section.http://militarianz.freeforums.org/wwii-uniforms-f26.html
Although, the Canadian Army also wore slouch hats during some eras, and so did the British during WW2 !, but the same comments would also apply to them, so factor in what you know about your relative and his locations, and then take your pick. !
If he spent his life in Britain the easiest and most certain solution would be to apply for his service record from the U.K. M.O.D..