This seems to be a distinctive cricket not matching any in the CNM field guide. After a search through A Guide to Crickets of Australia (Rentz) it looks very similar to Loxoblemmus pallens (p75-76), however some of the facial markings are slightly different and that species is not known to be in NSW or ACT. I am suggesting this is most likely a Loxoblemmus species.
Trevor, I'm not familiar with this genus and am sending your picture to You-ning for comment although I'm not sure if he has access to the collection at CSIRO.
I have been in touch with Youning Su, co-author of Field Guide to Crickets of Australia, and he has identified this sighting as mid instar female Lepidogryllus sp. He says it is either L comparatus, or L parvulus, but that the two species are indistinguishable, even as adults. He agrees it looks similar to Loxoblemmus pallens, but you can see the lower lateral lobe white area is different.