Hi Ross, The coastal heath habitat certainly sounds right for this species, but your critter seems to have an extra cream patch in the wing compared with pictures in our butterfly field guide and images on the web, so I'm going to pass on this and let the specialists have at it.
Thanks Jacki and Max. I wasn't able to get a photo of the wings fully spread. That would have helped. Looking in my field guide, the soma would be more interesting as the guide suggests its range is further south.
Hi Ross, Going through the unidentified butterflies and looking again at your sighting ; I've confirmed my original suggestion, as it really seems to be the best option.